Legume abundance along successional and rainfall gradients in Neotropical forests

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The size of the terrestrial carbon (C) sink is mediated by the availability of nutrients that limit plant growth. However, nutrient controls on primary productivity are poorly understood in the geographically extensive yet understudied tropical dry forest biome. To examine how nutrients influence above‐ and belowground biomass production in a secondary, seasonally dry tropical forest, we conducted a replicated, fully factorial nitrogen (N) and phosphorus (P) fertilization experiment at the stand scale in Guanacaste, Costa Rica. The production of leaves, wood, and fine roots was monitored through time; root colonization by mycorrhizal fungi and the abundance of N‐fixing root nodules were also quantified. In this seasonal forest, interannual variation in rainfall had the largest influence on stand‐level productivity, with lower biomass growth under drought. By contrast, aboveground productivity was generally not increased by nutrient addition, although fertilization enhanced growth of individual tree stems in a wet year. However, root growth increased markedly and consistently under P addition, significantly altering patterns of stand‐level biomass allocation to above‐ vs. belowground compartments. Although nutrients did not stimulate total biomass production at the community scale, N‐fixing legumes exhibited a twofold increase in woody growth in response to added P, accompanied by a dramatic increase in the abundance of root nodules. These data suggest that the relationship between nutrient availability and primary production in tropical dry forest is contingent on both water availability and plant functional diversity.

Section: Methodsmentioning

confidence: 99%

Plant community responses to stand‐level nutrient fertilization in a secondary tropical dry forest

Waring

Peréz‐Aviles

Murray

et al. 2019

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“…Yet, even when metrics did not shift significantly with succession (e.g., nitrification, N mineralization, litter N: P, and foliar P), this usually reflected consistently low rates of change rather than the effect of large variance among studies. This trend suggests that N recuperation, likely driven by symbiotic and free-living N 2 fixation (Sullivan et al 2014), may be common across the lowland tropics despite wide variations in N 2 -fixing legume abundance among sites (Losos and Leigh 2004) and the lower abundance of legumes in moist and wet forest relative to dry forest (Gei et al 2018). 3).…”

Section: Soil Ordermentioning

confidence: 98%

Biogeochemical recuperation of lowland tropical forest during succession

Sullivan

Nifong

Nasto

et al. 2019

Self Cite

2019. Biogeochemical recuperation of lowland tropical forest during succession. Ecology 100(4):Abstract. High rates of land conversion and land use change have vastly increased the proportion of secondary forest in the lowland tropics relative to mature forest. As secondary forests recover following abandonment, nitrogen (N) and phosphorus (P) must be present in sufficient quantities to sustain high rates of net primary production and to replenish the nutrients lost during land use prior to secondary forest establishment. Biogeochemical theory and results from individual studies suggest that N can recuperate during secondary forest recovery, especially relative to P. Here, we synthesized 23 metrics of N and P in soil and plants from 45 secondary forest chronosequences located in the wet tropics to empirically explore (1) whether there is a consistent change in nutrients and nutrient cycling processes during secondary succession in the biome; (2) which metrics of N and P in soil and plants recuperate most consistently; (3) if the recuperation of nutrients during succession approaches similar nutrient concentrations and fluxes as those in mature forest in~100 yr following the initiation of succession; and (4) whether site characteristics, including disturbance history, climate, and soil order are significantly related to nutrient recuperation. During secondary forest succession, nine metrics of N and/or P cycling changed consistently and substantially. In most sites, N concentrations and fluxes in both plants and soil increased during secondary succession, and total P concentrations increased in surface soil. Changes in nutrient concentrations and nutrient cycling processes during secondary succession were similar whether mature forest was included or excluded from the analysis, indicating that nutrient recuperation in secondary forest leads to biogeochemical conditions that are similar to those of mature forest. Further, of the N and P metrics that recuperated, only soil total P and foliar d 15 N were strongly influenced by site characteristics like climate, soils, or disturbance history. Predictable nutrient recuperation across a diverse and productive ecosystem may support future forest growth and could provide a means to quantify successful restoration of ecosystem function in secondary tropical forest beyond biomass or species composition.

“…In arid ecosystems N 2 -fixer abundance (both absolute and relative to nonfixers) and SNF activity increase with soil moisture (Schulze et al 1991, Aranibar et al 2004, Soper et al 2015; yet N 2 -fixers are more abundant in dry areas of the neotropics (Gei et al 2018) and North America (Liao et al 2017). If the marginal benefit of SNF vs. soil N uptake is diminished, N 2 -fixers may not compete with nonfixers as well and experience reduced abundance in early successional forests.…”

Section: Introductionmentioning

confidence: 99%

Drought sensitivity of an N₂‐fixing tree may slow temperate deciduous forest recovery from disturbance

Minucci

Miniat

Wurzburger

2019

Increased drought intensity and frequency due to climate change may reduce the abundance and activity of nitrogen (N 2 )-fixing plants, which supply new N to terrestrial ecosystems. As a result, drought may indirectly reduce ecosystem productivity through its effect on the N cycle. Here, we manipulated growing season net rainfall across a series of plots in an early successional mesic deciduous forest to understand how drought affects the aboveground productivity of the N 2 -fixing tree Robinia pseudoacacia and three co-occurring nonfixing tree species. We found that lower soil moisture was associated with reduced productivity of R. pseudoacacia but not of nonfixing trees. As a result, the relative biomass and density of R. pseudoacacia declined in drier soils over time. Greater aboveground biomass of R. pseudoacacia was also associated with greater total soil N, extractable inorganic N, N mineralization rates, and productivity of nonfixing trees. These soil N effects may reflect current N 2 fixation by R. pseudoacacia saplings, or the legacy effect of former trees in the same location. Our results suggest that R. pseudoacacia promotes the growth of nonfixing trees in early succession through its effect on the N cycle. However, the sensitivity of R. pseudoacacia to dry soils may reduce N 2 fixation under scenarios of increasing drought intensity and frequency, demonstrating a mechanism by which drought may indirectly diminish potential forest productivity and recovery rate from disturbance.