Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP)

Most land surface models (LSMs), the land components of Earth system models (ESMs), include representation of N limitation on ecosystem productivity. However only few of these models have incorporated phosphorus (P) cycling. In tropical ecosystems, this is likely to be particularly important as N tends to be abundant but the availability of rock-derived elements, such as P, can be very low. Thus, without a representation of P cycling, tropical forest response in areas such as Amazonia to rising atmospheric CO2 conditions remains highly uncertain. In this study, we introduced P dynamics and its interactions with the N and carbon (C) cycles into the Joint UK Land Environment Simulator (JULES). The new model (JULES-CNP) includes the representation of P stocks in vegetation and soil pools, as well as key processes controlling fluxes between these pools. We evaluate JULES-CNP at the Amazon nutrient fertilization experiment (AFEX), a low fertility site, representative of about 60 % of Amazon soils. We apply the model under ambient CO2 and elevated CO2. The model is able to reproduce the observed plant and soil P pools and fluxes under ambient CO2. We estimate P to limit net primary productivity (NPP) by 24 % under current CO2 and by 46 % under elevated CO2. Under elevated CO2, biomass in simulations accounting for CNP increase by 10 % relative to at contemporary CO2, although it is 5 % lower compared with CN and C-only simulations. Our results highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon forest with low fertility soils

Direct evidence for phosphorus limitation on Amazon forest productivity

The productivity of rainforests growing on highly weathered tropical soils is expected to be limited by phosphorus availability1. Yet, controlled fertilization experiments have been unable to demonstrate a dominant role for phosphorus in controlling tropical forest net primary productivity. Recent syntheses have demonstrated that responses to nitrogen addition are as large as to phosphorus2, and adaptations to low phosphorus availability appear to enable net primary productivity to be maintained across major soil phosphorus gradients3. Thus, the extent to which phosphorus availability limits tropical forest productivity is highly uncertain. The majority of the Amazonia, however, is characterized by soils that are more depleted in phosphorus than those in which most tropical fertilization experiments have taken place2. Thus, we established a phosphorus, nitrogen and base cation addition experiment in an old growth Amazon rainforest, with a low soil phosphorus content that is representative of approximately 60% of the Amazon basin. Here we show that net primary productivity increased exclusively with phosphorus addition. After 2 years, strong responses were observed in fine root (+29%) and canopy productivity (+19%), but not stem growth. The direct evidence of phosphorus limitation of net primary productivity suggests that phosphorus availability may restrict Amazon forest responses to CO2 fertilization4, with major implications for future carbon sequestration and forest resilience to climate change.The authors acknowledge funding from the UK Natural Environment Research Council (NERC), grant number NE/L007223/1. This is publication 850 in the technical series of the BDFFP. C.A.Q. acknowledges the grants from Brazilian National Council for Scientific and Technological Development (CNPq) CNPq/LBA 68/2013, CNPq/MCTI/FNDCT no. 18/2021 and his productivity grant. C.A.Q., H.F.V.C., F.D.S., I.A., L.F.L., E.O.M. and S.G. acknowledge the AmazonFACE programme for financial support in cooperation with Coordination for the Improvement of Higher Education Personnel (CAPES) and the National Institute of Amazonian Research as part of the grants CAPES-INPA/88887.154643/2017-00 and 88881.154644/2017-01. T.F.D. acknowledges funds from FundacAo de Amparo a Pesquisa do Estado de SAo Paulo (FAPESP), grant 2015/50488-5, and the Partnership for Enhanced Engagement in Research (PEER) programme grant AID-OAA-A-11-00012. L.E.O.C.A. thanks CNPq (314416/2020-0)

Rapid responses of root traits and productivity to phosphorus and cation additions in a tropical lowland forest in Amazonia

• Soil nutrient availability can strongly affect root traits. In tropical forests, phosphorus (P) is often considered the main limiting nutrient for plants. However, support for the P paradigm is limited, and N and cations might also control tropical forests functioning. • We used a large‐scale experiment to determine how the factorial addition of nitrogen (N), P and cations affected root productivity and traits related to nutrient acquisition strategies (morphological traits, phosphatase activity, arbuscular mycorrhizal colonisation and nutrient contents) in a primary rainforest growing on low‐fertility soils in Central Amazonia after one year of fertilisation. • Multiple root traits and productivity were affected. Phosphorus additions increased annual root productivity and root diameter, but decreased root phosphatase activity. Cation additions increased root productivity at certain times of year, also increasing root diameter and mycorrhizal colonisation. P and cation additions increased their element concentrations in root tissues. No responses were detected with N addition. • Here we show that rock‐derived nutrients determine root functioning in low‐fertility Amazonian soils, demonstrating not only the hypothesised importance of P, but also highlighting the role of cations. The changes in fine root traits and productivity indicate that even slow‐growing tropical rainforests can respond rapidly to changes in resource availability

Functional diversity and trait filtering of insectivorous bats on forest islands created by an Amazonian mega dam

Mega dams in lowland tropical forests often create large archipelagos, leading to biodiversity decay and disruption of ecosystem functioning in remnant habitat islands. We investigated the functional diversity and functional trait filtering of aerial insectivorous bats in both insular forest patches created by a vast ~30-year-old hydropower reservoir and the adjacent mainland continuous forest in Central Amazonia. Bats were surveyed using passive bat recorders across 34 forest sites. Based on a set of morphological traits derived for each species recorded, we estimated both the bat functional richness, functional evenness and functional dispersion at each surveyed site. We further assessed the effects of local vegetation, patch and landscape features on patterns of functional diversity. The interaction between functional traits, environmental characteristics, and species distribution was investigated using a combination of RLQ and fourth-corner analyses. We found that mainland sites retained higher functional richness and lower functional evenness compared to forest islands, indicating a more complete functional assemblage in the mainland. Additionally, species composition was affected by local vegetation structure and forest area, with small isolated islands exhibiting pervasive loss of functional traits. RLQ and fourth-corner analyses showed that larger understorey foraging species with greater dispersal capacity, constant frequency–frequency modulated calls, and higher frequency of maximum energy were associated with more isolated small islands. Conversely, forest subcanopy species, exhibiting quasi-constant frequency calls and presenting low dispersal capacity were associated with continuous forests and islands with greater forest area, and were therefore more sensitive to habitat insularization. Our study calls attention to the pervasive impacts induced by large dams on the functional diversity of tropical insectivorous bats. We recommend that future assessments of the effects of habitat fragmentation on mammals should include traits linked to ecosystem services. In designing and licensing new dams, we suggest the creation of extensive protected areas surrounding mainland forests to minimize the detrimental impacts of small isolated islands and safeguard the full complement of key ecological functions provided by insectivorous bats. Read the free Plain Language Summary for this article on the Journal blog

Aerial insectivorous bat responses to 30 years of forest insularization in a dam-created Amazonian archipelagic landscape

Mega dams result in habitat loss and fragmentation in lowland tropical forests, compromising the diversity and ecosystem functioning in remnant habitat islands. We investigated the structure of aerial insectivorous bat assemblages within insular forest patches created by a vast ∼30-year-old hydropower reservoir and adjacent mainland continuous forests in Central Amazonia. Bats were surveyed using passive bat recorders across 34 sites. We assessed bat assemblage responses to landscape insularization and estimated the contribution of assemblage-wide components of β-diversity. Additionally, we assessed the effects of local vegetation, and both patch and landscape variables on bat species diversity. Continuous forest sites in the mainland retained higher species richness and bat activity compared to islands, leading to divergent species composition between forest sites. Larger islands (>100 ha) and continuous forests tended to share a similar assemblage composition manly drive by species richness differences with a minor contribution of species replacements. Moreover, local vegetation structure, island size, and landscape edge area exerted significant effects on species richness, bat activity, and species composition, with small degraded islands and landscapes dominated by forest edges exhibiting pervasive species loss. Our study highlights the detrimental impacts of forest fragmentation induced by large dams on aerial insectivorous bat assemblages. If new dam projects are inevitable, we recommend the creation of extensive protected areas in land-bridge island systems and their adjacent continuous forests. Those protected sites can minimize the negative impacts of small islands, safeguarding forest quality for forest-dependent bats, which ensures the continuity of their ecosystem services