The influence of herbivore generated inputs on nutrient cycling and soil processes in a lower montane tropical rain forest of Puerto Rico

The role of insect herbivores in the nutrient cycling dynamics of forest ecosystems remains poorly understood. Although past research in herbivory has focused primarily on the deleterious effects that insects can have on tree growth and mortality, the overall effects of herbivory are more complex. Herbivores have the potential to alter key ecosystem processes in a number of ways. One is by altering the flow of nutrients from the canopy to the forest floor. The studies presented here examine the effects that frass (insect excreta), greenfall (green leaf fragments) and herbivore modified throughfall, have on decomposition processes and soil nutrient dynamics. Both studies were carried out in a lower montane tropical rain forest near the El Verde Field Station, Luquillo Long-Term Ecological Research (LTER) site, Puerto Rico. The first study presented here tested the hypotheses that green leaves are of higher quality and decompose more rapidly than senesced leaves. Green and senesced leaves of four common native tree species (Dacryodes excelsa, Manilkara bidentata, Guarea guidonia and Cecropia schreberiana), were collected and analyzed for C, N, and complex C compounds. Litterbags containing green and senescent leaves of each species were placed in the field for up to 16 weeks in order to compare rates of litter decomposition. Green leaves contained significantly higher (p < 0.05) concentrations of N and lower lignin:N ratios than senescent leaves for all four species. Decomposition rates were significantly higher (p < 0.05) for green leaves compared to senescent leaves for all four species. These results demonstrate that insect herbivores may influence key ecosystem processes via the production of greenfall. The relevance of this study extends to green leaf deposition resulting from multiple sources, including high wind and rain events, as well as disturbance by larger canopy organisms. The second study tested a direct link between herbivory and soil processes. By altering levels of herbivory on a common understory plant (Piper glabrescens), using a prevalent folivore (Lamponius portoricensis), this study tested for effects of herbivory on nutrient inputs to the soil, as well as rates of litter decomposition. Enclosures were constructed around P. glabrescens individuals in the field and assigned to one of four treatments: herbivore exclusion, control, low herbivory and high herbivory. Total leaf area loss and greenfall production were measured for each plant using a sub-sample of randomly chosen leaves. Litterbags and ion exchange resin bags, placed under each plant, recorded rates of litter decomposition and the flow of NO3, NH4 and PO4 to the forest floor during this 76-day experiment. The treatments were effective in establishing a wide range of herbivory. Both the total leaf area removed and greenfall deposition demonstrated significant positive correlations (p <0.05) with NO3 transfer to the forest floor, but not with NH4 or PO4. Although decomposition rates showed no significant correlation with total leaf area losses or the greenfall component, a significant correlation was found between decay rates and frass related inputs (defined as the total leaf area removed minus the portion removed as greenfall). This study clearly demonstrates the ability of insect herbivores to alter nutrient cycling in tropical forest ecosystems and is the first study to demonstrate a direct link between herbivory and decomposition processes. These experiments provide clear evidence that insect herbivores can alter nutrient cycling and soil processes in forest systems. Such findings elucidate the need to more fully consider the effects of herbivores in both ecosystem models and management issues of tropical forest ecosystems

Dataset associated with "Artefactual depiction of predator–prey trophic linkages in global soils"

This database contains results from an exploratory literature search (carried out over May-July 2020) to detect the trophic linkages that departed from an initial set of 36 common soil-dwelling invertebrate taxa (i.e., in the capacity of either predator or prey items). It consists of a non-exhaustive list of macro-, meso- and micro-fauna which did not necessarily include all common soil fauna (e.g., Amphipoda). For each literature record, we logged the resource and consumer organisms for each trophic linkage. For generalist (i.e., polyphagous) predators that foraged within/on soil substrates, we logged all trophic linkages that were outlined in each literature record (i.e., involving other organisms beyond the initial set of 36 taxa). Taxa were identified either at the taxonomic hierarchy of phylum, sub-class or order and comprised a diverse set of common, globally-distributed soil-foraging biota.Soil invertebrates contribute to multiple ecosystem services, including pest control, nutrient cycling, and soil structural regulation, yet trophic interactions that determine their diversity and activity in soils remain critically understudied. Here, we systematically review literature (1966–2020) on feeding habits of soil arthropods and macrofauna and summarize empirically studied predator–prey linkages across ecosystem types, geographies and taxa. Out of 522 unique predators and 372 prey organisms (constituting 1947 predator–prey linkages), the vast majority (> 75%) are only covered in a single study. We report a mean of just 3.0 ± 4.7 documented linkages per organism, with pronounced taxonomic biases. In general, model organisms and crop pests (generally Insecta) are well-studied, while important soil-dwelling predators, fungivores and detritivores (e.g., Collembola, Chilopoda and Malacostraca) remain largely ignored. We argue that broader food-web based research approaches, considering multiple linkages per organism and targeting neglected taxa, are needed to inform science-driven management of soil communities and associated ecosystem services

Dataset associated with "Land use conversion to agriculture impacts biodiversity, erosion control and key soil properties in an Andean watershed"

This data set involves soil and plant variables collected from 50 farm and forest plots in a mountainous region of the Valle del Cauca Department of Colombia. Sampling was conducted in 2016 to evaluate soil biodiversity and ecosystem services provided across five dominant land uses in the region.The conversion of natural vegetation to agricultural land uses in mountainous Andean landscapes threatens an array of key ecological processes and ecosystem services. In protected areas and buffer regions that provide water to cities, it is critical to understand how interactions between plants and soil communities sustain a range of ecosystem functions, associated with nutrient recycling, soil structure, and erosion control. We sought to understand how land use conversion within a mountainous tropical forest landscape influences the diversity of vegetation and soil macrofauna communities, soil physico-chemical properties, and hydrological regulation services. Biodiversity and a suite of key soil-based ecosystem services were compared in five major land uses of the Cali River watershed: 1) annual cropping systems, 2) coffee plantations, 3) pastures, 4) abandoned shrubland, and 5) secondary forests. The diversity of woody and herbaceous vegetation, as well as soil macrofauna was assessed in each land use. Soil chemical fertility and aggregate morphology were assessed via laboratory analyses and visual separation of soil aggregates based on their origin. Infiltration, runoff, and sediment production were measured using a portable rainfall simulator. We found a decrease in the diversity of woody vegetation across land-uses to be associated with lower diversity of soil macrofauna. At the same time, agricultural management, annual crops in particular, supports the largest earthworm populations, likely due to increased organic inputs and low impact tillage, which appears not to diminish soil fertility and water infiltration. In contrast, the low soil fertility in pastures was associated with the lowest values of soil C, poor aggregation, and high bulk density, and likely reflects overgrazing, with negative implications for water infiltration and erosion. Associations between the different sets of variables, evaluated with a co-inertia analysis, highlights the hierarchical relevance of plant cover and woody diversity on ecosystem services. The biological complexity associated with intact forest cover appears to generate "bundles" of co-occurring ecosystem services, with this land use demonstrating the highest infiltration, and low runoff and sediment losses. Our findings demonstrate that forests and tree-based agricultural systems may better contribute to the provision of multiple ecosystem services, including biodiversity conservation and hydrologic regulation

Las mezclas de gramíneas y leguminosas muestran el potencial de aumentar la producción de biomasa aérea y subterránea en los barbechos andinos basados en el forraje

Descargue el texto completo en el portal de la revista Agronomy: https://doi.org/10.3390/agronomy12010142Los suelos altoandinos están amenazados por la intensificación de los sistemas de cultivo. Los barbechos mejorados basados en el forraje ofrecen una gran promesa para abordar este problema, pero es necesario investigar para entender mejor el potencial de las mezclas de especies frente a los monocultivos para apoyar múltiples objetivos de los agricultores, especialmente la producción de forraje y la conservación del suelo. Hemos utilizado un estudio en maceta para cuantificar la producción de biomasa aérea y subterránea, así como la absorción total de N de las mezclas de gramíneas y leguminosas entre cinco gramíneas: (1) avena (Avena sativa), (2) ryegrass (Lolium multiflorum), (3) festulolium (Lolium × Festuca genera), (4) bromo (Bromus catharticus), y (5) hierba de la huerta (Dactylis glomerata), y cuatro leguminosas: (1) veza (Vicia dasycarpa), (2) trébol rojo (Trifolium pratense), (3) medicago negro (Medicago lupulina), y (4) alfalfa (Medicago sativa) en relación al rendimiento de cada especie en monocultivo dentro de dos suelos de los Andes centrales peruanos. Los bicultivos de gramíneas y leguminosas demostraron un rendimiento superior, produciendo un 65% y un 28% más de biomasa seca total y de absorción total de N en promedio que los monocultivos. La biomasa aérea de los bicultivos estuvo significativamente influenciada por la especie de leguminosa presente, mientras que la biomasa subterránea estuvo más afectada por la especie de hierba en la mezcla. Al evaluar el crecimiento de cada especie por separado, nuestros resultados indican que el exceso de rendimiento fue impulsado más por el mayor crecimiento de las gramíneas en relación con las leguminosas. Nuestros resultados indican que la combinación de grupos funcionales clave (p. ej., gramíneas y leguminosas, anuales y perennes) es muy prometedora para el desarrollo de barbechos mejorados que apoyen la salud del suelo y la productividad en los agroecosistemas andinos.Soils of the Andean highlands are under threat from cropping system intensification. Improved forage-based fallows offer great promise to address this issue, but research is needed to better understand the potential of species mixtures vs. monocultures to support multiple farmer objectives, especially forage production and soil conservation. We used a pot study to quantify above- and belowground biomass production as well as the total N uptake of grass–legume pairs between five grasses: (1) oat (Avena sativa), (2) ryegrass (Lolium multiflorum), (3) festulolium (Lolium × Festuca genera), (4) brome grass (Bromus catharticus), and (5) orchard grass (Dactylis glomerata), and four legumes: (1) vetch (Vicia dasycarpa), (2) red clover (Trifolium pratense), (3) black medic (Medicago lupulina), and (4) alfalfa (Medicago sativa) relative to the performance of each species in monoculture within two soils from the central Peruvian Andes. Grass–legume bicultures demonstrated significant overyielding, producing 65% and 28% more total dry biomass and total N uptake on average than monocultures. Aboveground biomass of bicultures was significantly influenced by the species of legume present, while belowground biomass was more affected by the grass species in the mixture. When evaluating the growth of each species separately, our findings indicate that overyielding was driven more by the enhanced growth of grasses relative to legumes. Our findings indicate that combining key functional groups (e.g., grass and legume, annual and perennial) offers great promise for developing improved fallows for supporting soil health and productivity in Andean agroecosystems

Inter-community and on-farm asymmetric organic matter allocation patterns drive soil fertility gradients in a rural Andean landscape

Soil fertility in agricultural landscapes is driven by complex interactions between natural and anthropogenic processes, with organic matter (OM) inputs playing a critical role. Asymmetric allocation patterns of these resources among communities and within individual farms can lead to soil fertility gradients. However, the drivers and consequences of such patterns in different socioecological contexts remains poorly documented and understood. The objective of this study was to address this gap by assessing asymmetric OM allocation patterns and the associated consequences for soil fertility management in three indigenous communities located in the Central Ecuadorian Andes. We found that both distance from homestead and perception of fertility were associated with asymmetric OM allocation patterns to fields as well as with soil fertility gradients within farms. For example, soil organic carbon (SOC), total nitrogen (N), available phosphorus (P), and exchangeable potassium (K) all decreased with distance from the homestead, while SOC, total N, and available P were positively correlated with a farmer's perception of soil fertility. We note that these fertility gradients remained even in the case of increased farm-level OM inputs. Overall OM allocation patterns differed significantly among communities and were associated with significant differences in soil fertility, with the highest levels of available P and exchangeable K found in the community with the highest OM inputs. The results of this study indicate the importance of asymmetric OM allocation patterns encountered at different scales, both within farms and among neighboring communities, in rural Andean landscapes and their significant interactions with soil fertility gradients.</p

Live barriers and associated organic amendments mitigate land degradation and improve crop productivity in hillside agricultural systems of the Ecuadorian Andes

Land degradation caused by erosion and nutrient depletion in the Andes poses serious existential threats to small-scale farming. Although the potential of hedgerows to decrease water erosion is well recognised, their potential dual-use as a source of organic amendments to supplement farmer inputs is much less studied. The objective of this investigation was therefore to explore locally developed options for hedgerows that address these twin challenges. Experimental plots were installed to assess water erosion control by hedgerows and the effect of organic amendments harvested from the hedgerows on soil productivity, soil moisture, and soil fertility over the course of 2 years and three crop cycles (two of barley and one of rye). The experiment was conducted in two sites within the community at distinct elevations and associated biophysical contexts. At each site, four treatments were established, comparing a control treatment versus three types of hedgerows: (a) Andean alder, (b) canary grass strips, and (c) mixed canary grass and Andean alder. Results demonstrated that hedgerows and associated organic inputs comprised canary grass, and mixed canary grass and Andean alder reduced water erosion by 50–60% and increased biomass production by up to 1.1 Mg ha−1 and grain yield by up to 0.5 Mg ha−1. We conclude that although hedgerows are unlikely to produce sufficient quantities of organic resources to satisfy all nutrient input requirements, their potential to decrease erosion and supplement existing organic matter inputs indicates that they should be strongly considered as an option for improved agricultural management within this and similar resource constrained contexts.</p

Traditional soil fertility management ameliorates climate change impacts on traditional Andean crops within smallholder farming systems

Global changes, particularly rising temperatures, threaten food security in smallholder mountain communities by impacting the suitability of cultivation areas for many crops. Land-use intensification, associated with agrochemical use and tillage threaten soil health and overall agroecosystem resilience. In the Andean region, farmers often cultivate crops at multiple elevations. Warming climates have led to a shift in cultivation upslope, but this is not feasible in many areas. Traditional soil fertility management practices together with a focus on traditional (orphan) crops offers promise to cope with rapid climate warming in the region. To understand the impacts of warming and changing nutrient management, we established two side-by-side experiments using the traditional Andean crops Oxalis tuberosa (Oca) and Lupinus mutabilis (Tarwi) at three elevations, each with two fertility treatments (organic and synthetic). Soil and climate data (i.e., temperature and precipitation) were collected throughout the growing season, and crop performance was evaluated through impacts on yield and other growth metrics (e.g., biomass, pest incidence). We used two-way ANOVA to assess the influence of site (elevation) and management type (organic vs. synthetic) on crop performance. Results indicated that warmer climates (i.e., lowest elevation) negatively impact the production and performance of O. tuberosa, but that organic fertilization (sheep manure) can help maintain crop yield and biomass production in warmer conditions relatively to synthetic nutrient inputs. In contrast, L. mutabilis showed accelerated growth in warmer conditions, but grain yield and biomass production were not significantly affected by site and showed no interaction with nutrient management. Our findings highlight that climate warming represents a serious threat to small-scale crop production in the Peruvian Andes and could cause severe declines in the production of locally important crops. Additionally, the continued reliance traditional crops with organic inputs, instead of synthetic fertilizers, may help support agricultural productivity and resilience under climate change

Earthworms regulate plant productivity and the efficacy of soil fertility amendments in acid soils of the Colombian Llanos

The Llanos region of Colombia represents one of the last large agricultural frontiers and is undergoing a rapid conversion from naturalized savanna to intensive agriculture with high agrochemical inputs and tillage. This massive land-use conversion has considerable impact on ecosystem services and biodiversity, particularly soil macrofauna, yet the full implications of this land-use shift for long-term agroecosystem productivity are poorly understood. To better elucidate potential land-use change impacts on agricultural production we used experimental microcosms in the greenhouse to evaluate how the common earthworm, Pontoscolex corethrurus, influences plant growth, nutrient uptake, and key soil properties relative to the application of lime and P fertilizer, both common soil fertility amendments in the region. Additionally, we aimed to explore the potential for interactions between earthworms and these amendments across distinct plant types, the grass Brachiaria decumbens and the legume Phaseolus vulgaris, which display different rooting patterns and nutrient acquisition strategies. Earthworms increased the biomass production of B. decumbens by 180% and N uptake by more than 240%, while P fertilizers and lime additions increased total biomass by less than 30% each for B. decumbens. Effects on P. vulgaris were similar, but less pronounced with earthworms increasing total biomass production by 35% and total plant N content by 70%, while neither lime nor P alone significantly influenced total biomass or N uptake. However, a significant interaction between earthworms and lime enhanced total biomass N content of P. vulgaris by more than 150% relative to microcosms without P. corethrurus, suggesting that earthworms can greatly enhance the efficacy of lime in soils. Additionally, we found that earthworms greatly improved soil aggregation, but only in the presence of plants, and that this effect was most prominent in microcosms with P. vulgaris. When testing treatment effects on soil P availability, only fertilizer P additions significantly influenced resin P, but not microbial biomass P. Our findings suggests the importance of developing management strategies that promote the activity and diversity of earthworms and other soil biota as a means to enhance crop productivity, resource use efficiency and a range of soil-based ecosystem services in the Llanos region and beyond

Drivers of growth and establishment of the invasive plant Rumex acetosella within Andean fallow systems

Intensification of crop rotations and associated agricultural practices are reducing the capacity of traditional fallows to restore soil fertility and provide forage in Andean cropping systems. While the implementation of improved fallows offers great promise to enhance forage provision and maintain soil productivity, effects of these practices on the establishment of problematic weeds, including non-native plant species, remain poorly understood. To address this knowledge gap, we studied: i) how biotic and abiotic environmental factors influence the establishment and productivity of weeds in traditional fallows; and ii) to what extent improved fallows can help control weedy vegetation in smallholder rotations of the high Andes. Specifically, in this research, we focused on the invasive plant species Rumex acetosella L., which is a common concern of farmers throughout the central Peruvian Andes. We leveraged a multi-site, participatory research trial established in 2017 across eight communities in the region to understand the main drivers of R. acetosella presence and productivity. We used a total of 82 sites, each with paired treatments of traditional fallow (control with natural revegetation) and improved fallow (seeded with Vicia sativa L. and Avena sativa L.). Prior to treatment establishment we measured soil texture, pH, soil organic matter content as well as exchangeable macro-nutrients. Vegetation data was recorded in each treatment and divided into four categories: 1) A. sativa, 2) V. sativa, 3) R. acetosella, and 4) other weeds, and weighed to determine the relative biomass contribution of each. From these data, we calculated an index for R. acetosella pressure, weed pressure, and forage productivity. Our findings indicate that improved fallows greatly suppress weedy vegetation relative to unmanaged controls, including the invasive R. acetosella. Multivariate analyses suggested that R. acetosella abundance was associated with the presence of other non-planted weeds and predictors of soil fertility. The mean R. acetosella index in improved fallows was significantly lower compared to traditional fallows. We found R. acetosella biomass to be greater at lower productivity sites, i.e., those at higher elevations with cooler climates and sites with less fertile soils. Our findings indicate that if the fallow portion of a rotation is kept productive via adequate soil fertility inputs, the biomass of weeds, including the alien R. acetosella, is dramatically reduced