Effects of canopy closure on photosynthetic characteristics of Ilex latifolia Thunb. in Phyllostachys pubescens forests

Plantation under the forest is a good way of agroforestry, but the canopy closure has a great influence on understory herbs’ growth. In the study, different canopy closures of Phyllostachys pubescens forests were set up to explore its influence on the growth of Ilex latifolia Thunb. The photosynthetic characteristics of Ilex latifolia leaves under different canopy closures were determined by Li-6400 portable photosynthetic system. The results showed that the net photosynthetic rate curve of Ilex latifolia leaves of T1 (canopy closure of 0.56) was bimodal with an obvious "midday depression" phenomenon, while the net photosynthetic rate curves of T2 (canopy closure of 0.72) and T3 (canopy closure of 0.86) were unimodal. The results of light response curve showed that the photosynthetically active radiation and transpiration rate reduced with the increasing of canopy closures. The photosynthetically active radiation, transpiration rate, stomatal conductance, and net photosynthetic rate of Ilex latifolia leaves of T2 were higher than those of T3. Although the net photosynthetic rate of T2 was lower than that of T1, it had no obvious photo-inhibition which affected plant growth. Overall, the canopy closure of 0.72 was more suitable for the growth of Ilex latifolia. The herb plantation in the bamboo forest should be considered with the canopy closure for a better growth

Human Disturbance Reduces Plant Species Diversity and Stability of Phyllostachys pubescens Forests

Plant species diversity is an important index reflecting the functional complexity and stability of ecosystems. Human activity can completely alter plant species diversity and cause serious degradation of ecosystems but its impact on bamboo forest still lacks of systematic evaluation. In this study, we performed a field investigation to reveal the influences of human disturbances on the plant diversity and stability of Moso bamboo forests at Southern China. The selected bamboo fields contained different intensities of human activities that could be classified as slight, moderate and severe disturbance level. Species richness index S, Shannon-Wienner index H, Simpson index D, Pielou index Jsw, community similarity index IS and community stability index were employed to quantitatively evaluate the plant species diversity and stability. The survey revealed that there were 203 species belonging to 83 families and 108 genera in Moso bamboo forests. The number of plant species in the Moso bamboo forests decreased with the increasing of disturbance intensity. The species diversity indexes generally followed the order of slight > moderate > severe disturbance, as well as the richness index S, Shannon-Wienner index H and Pielou index Jsw. The similarity and species stability of the bamboo forest communities also decreased with the increase of the disturbance intensity. Under the severe disturbance, plant species replacement occurred strongly. The obtained results provide some a guideline for the sustainable management of bamboo forest

Effect of Land Cultivation on Soil Nutrient Sedimentation in Water at Southern China

Soil erosion associated with land cultivation exerts a great impact on ecological environment. Such an impact is specific of land, crop, tillage, management and so on. This study aimed to investigate the effects of crop cultivation on water quality by comparing nutrient distribution in the sediment at Southern China. Two sedimentation sites adjacent to the uncultivated (S1) and cultivated upland (S2) were selected and samples were analyzed. Results showed that soil pH decreased with the increasing depth above 20 cm and then kept relatively stable of the both sediments. Soil organic matter, nitrogen and phosphorus contents decreased with the increasing depth. There was no significant difference between two sediments in organic matter and nitrogen contents, but the total phosphorus and extractable phosphorus contents in S2 were much higher than that in S1. The data indicated that soil eroded from S2 could possess much high potential to deteriorate water quality. Nutrient sedimentation can reflect the history of soil erosion and provide useful information for sustainable soil management and water conservation through improving cultivation and tillage measures

Advances in Plant Auxin Biology: Synthesis, Metabolism, Signaling, Interaction with Other Hormones, and Roles under Abiotic Stress

Auxin is a key hormone that regulates plant growth and development, including plant shape and sensitivity to environmental changes. Auxin is biosynthesized and metabolized via many parallel pathways, and it is sensed and transduced by both normal and atypical pathways. The production, catabolism, and signal transduction pathways of auxin primarily govern its role in plant growth and development, and in the response to stress. Recent research has discovered that auxin not only responds to intrinsic developmental signals, but also mediates various environmental signals (e.g., drought, heavy metals, and temperature stresses) and interacts with hormones such as cytokinin, abscisic acid, gibberellin, and ethylene, all of which are involved in the regulation of plant growth and development, as well as the maintenance of homeostatic equilibrium in plant cells. In this review, we discuss the latest research on auxin types, biosynthesis and metabolism, polar transport, signaling pathways, and interactions with other hormones. We also summarize the important role of auxin in plants under abiotic stresses. These discussions provide new perspectives to understand the molecular mechanisms of auxin’s functions in plant development

Effects of Bamboo (Phyllostachys praecox) Cultivation on Soil Nitrogen Fractions and Mineralization

The mineralization of soil organic nitrogen (N) is the key process in the cycling of N in terrestrial ecosystems. Land-use change to bamboo (Phyllostachys praecox) cultivation that later entails organic material mulching combined with chemical fertilizer application will inevitably influence soil N mineralization (Nmin) and availability dynamics. However, the soil Nmin rates associated with various N fractions of P. praecox in response to land-use change and mulching are not well understood. The present study aimed to understand the effects of land-use change to P. praecox bamboo cultivation and organic material mulching on soil Nmin and availability. Soil properties and organic N fractions were measured in a P. praecox field planted on former paddy fields, a mulched P. praecox field, and a rice (Oryza sativa L.) field. Soil Nmin was determined using a batch incubation method, with mathematical models used to predict soil Nmin kinetics and potential. The conversion from a paddy field to P. praecox plantation decreased the soil pH, soil total N, and soil organic matter (SOM) content significantly (p < 0.05); the mulching method induced further soil acidification. The mulching treatment significantly augmented the SOM content by 7.08% compared with the no-mulching treatment (p < 0.05), but it decreased soil hydrolyzable N and increased the nonhydrolyzable N (NHN) content. Both the Nmin rate and cumulative mineralized N were lowest in the mulched bamboo field. The kinetics of Nmin was best described by the ‘two-pool model’ and ‘special model’. The Pearson’s correlation analysis and the Mantel test suggested soil pH was the dominant factor controlling the soil cumulative mineralized N and mineralization potential in the bamboo fields. These findings could help us better understand the N cycling and N availability under mulching conditions for shifts in land use, and provide a scientific basis for the sustainable management of bamboo plantations

Phenological changes offset the warming effects on biomass production in an alpine meadow on the Qinghai–Tibetan Plateau

Phenology is an important indicator of plant responses to environmental changes and is closely correlated with biomass production. However, how changes in phenological events affect plant biomass production when exposed to changing temperature and precipitation remain unclear. We conducted a 4-year manipulative experiment of warming and precipitation addition to explore phenology-biomass interactions under climate change in a dry alpine meadow on the central Qinghai-Tibetan Plateau from 2015 to 2018. In dry and warm years, warming delayed phenology and precipitation addition advanced them. Warming decreased the biomass of Kobresia pygmaea in 2018 and the biomass of Poa pratensis in 2015, 2017 and 2018. However, precipitation addition significantly increased the biomass of Poa pratensis and Potentilla multifida in most of the experimental years. Phenological changes regulated the responses of biomass to treatments. Specifically, delay of green up of P. pratensis and delay of withering of K. pygmaea induced by warming can increase biomass production, but it can be offset by the direct negative effects of warming on biomass. Synthesis. Here we show how warming-induced drought tend to decrease the biomass production of graminoids and the negative effects of warming on the biomass of P. pratensis and K. pygmaea were partially offset by green up postponement and withering postponement respectively. Our results highlights phenology is a crucial regulator for biomass production under climate change. Hence, both direct and indirect effects of warming and precipitation addition on phenology and biomass cannot be ignored when predicting biomass responses to climate change.National Natural Science Foundation of China12 month embargo; published 5 November 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Ecological Engineering Projects Shifted the Dominance of Human Activity and Climate Variability on Vegetation Dynamics

Global greening and its eco-environmental outcomes are getting mounting international focus. The important contribution of China to the global greening is highly appreciated. However, the basic driving forces are still elusive. The Loess Plateau (LP) and Three-River Source Region (TRSR) were chased as study areas in Northern China. The prior one represents the region experiencing intensive human interventions from ecological engineering projects, while the latter is a typical region that is experiencing faster climate change. Hypothesized to be driven by a disproportionate rate of human activities and climates, also being regions of typical large-scale ecological engineering projects, the study goal is to identify the actual driving forces on vegetation dynamics in these two regions. Trend analysis, correlation analysis, and residual trend-based method (RESTREND) were utilized to understand the relationships between climate variability, human activities, and vegetation dynamics. The spatiotemporal variations of vegetation from 1982 to 2019 were evaluated and the respective impacts of climatic and anthropogenic factors on vegetation dynamics were disentangled. Indicating apparent vegetation restoration in LP and TRSR, the results depict that annual LAI has remarkably increased during the 38 years. Temperature and precipitation promoted vegetation growth, whereas the solar radiation and vapor pressure deficit hampered it. After implementing the ecological engineering projects, the primary climatic factor changed from temperature to precipitation. Meanwhile, human activities act as the major driving factor in vegetation greening in the entire study area, with a contribution rate exceeding 70%. This information highlights that ecological engineering can significantly reduce the risks of ecosystem degradation and effectively restore vegetation, especially in ecologically sensitive and vulnerable areas

Ecological Engineering Projects Shifted the Dominance of Human Activity and Climate Variability on Vegetation Dynamics

Global greening and its eco-environmental outcomes are getting mounting international focus. The important contribution of China to the global greening is highly appreciated. However, the basic driving forces are still elusive. The Loess Plateau (LP) and Three-River Source Region (TRSR) were chased as study areas in Northern China. The prior one represents the region experiencing intensive human interventions from ecological engineering projects, while the latter is a typical region that is experiencing faster climate change. Hypothesized to be driven by a disproportionate rate of human activities and climates, also being regions of typical large-scale ecological engineering projects, the study goal is to identify the actual driving forces on vegetation dynamics in these two regions. Trend analysis, correlation analysis, and residual trend-based method (RESTREND) were utilized to understand the relationships between climate variability, human activities, and vegetation dynamics. The spatiotemporal variations of vegetation from 1982 to 2019 were evaluated and the respective impacts of climatic and anthropogenic factors on vegetation dynamics were disentangled. Indicating apparent vegetation restoration in LP and TRSR, the results depict that annual LAI has remarkably increased during the 38 years. Temperature and precipitation promoted vegetation growth, whereas the solar radiation and vapor pressure deficit hampered it. After implementing the ecological engineering projects, the primary climatic factor changed from temperature to precipitation. Meanwhile, human activities act as the major driving factor in vegetation greening in the entire study area, with a contribution rate exceeding 70%. This information highlights that ecological engineering can significantly reduce the risks of ecosystem degradation and effectively restore vegetation, especially in ecologically sensitive and vulnerable areas

Coarse spatial resolution remote sensing data with AVHRR and MODIS miss the greening area compared with the Landsat data in Chinese drylands

The warming-wetting climates in Chinese drylands, together with a series of ecological engineering projects, had caused apparent changes to vegetation therein. Regarding the vegetation greening trend, different remote sensing data had yielded distinct findings. It was critical to evaluate vegetation dynamics in Chinese drylands using a series of remote sensing data. By comparing the three most commonly used remote sensing datasets [i.e., MODIS, Advanced Very High Resolution Radiometer (AVHRR), and Landsat], this study comprehensively investigated vegetation dynamics for Chinse drylands. All three remote sensing datasets exhibited evident vegetation greening trends from 2000 to 2020 in Chinese drylands, especially in the Loess Plateau and Northeast China. However, Landsat identified the largest greening areas (89.8%), while AVHRR identified the smallest greening area (58%). The vegetation greening areas identified by Landsat comprise more small patches than those identified by MODIS and AVHRR. The MODIS data exhibited a higher consistency with Landsat than with AVHRR in terms of detecting vegetation greening areas. The three datasets exhibited high consistency in identifying vegetation greening in Northeast China, Loess Plateau, and Xinjiang. The percentage of inconsistent areas among the three datasets was 39.56%. The vegetation greening areas identified by Landsat comprised more small patches. Sensors and the atmospheric effect are the two main reasons responsible for the different outputs from each NDVI product. Ecological engineering projects had a great promotion effect on vegetation greening, which can be detected by the three NDVI datasets in Chinese drylands, thereby combating desertification and reducing dust storms