Foliar phosphorus fractions reveal how tropical plants maintain photosynthetic rates despite low soil phosphorus availability

Abstract

Nitrogen (N) and phosphorus (P) are essential nutrients for plant metabolism, and their availability often limits primary productivity. Whereas the effects of N availability on photosynthetic capacity are well established, we still know relatively little about the effects of P availability at a foliar level, especially in P‐limited tropical forests. We examined photosynthetic capacity, leaf mass per area (LMA) and foliar P fractions in five woody plant species after 6 years of N and P fertilization in a lowland tropical forest. Foliar N:P ratios indicated P limitation of the unfertilized plants; accordingly, photosynthetic P‐use efficiency (PPUE) and LMA decreased with P addition, and foliar N and P concentrations increased, whereas N addition had little effect on measured foliar traits. However, P addition enhanced photosynthetic capacity only in one species and not in other four species. We then assessed plant acclimation to low P availability by quantifying four fractions of foliar P representing different functional pools: structural P, metabolic P (including inorganic P), nucleic acid P, and residual P. We found that P addition enhanced the concentrations of metabolic, structural, and nucleic acid P fractions in all species, but the magnitude of the effect was species‐specific. Our findings indicate that tropical species acclimate to low P availability by altering allocation of foliar P to meet the demand of P for photosynthesis. Importantly, species typical of lowland tropical forests in East Asia maintained their photosynthetic rate under low P availability. We conclude that P limitation of leaf photosynthetic capacity may not be as common as previously assumed due to plant acclimation mechanisms in low‐P tropical forests. Species‐specific strategies to allocate P to different foliar fractions represent a potentially important adaptive mechanism for plants in P‐limited systems.

Small tropical forest trees have a greater capacity to adjust carbon metabolism to long‐term drought than large canopy trees

“…We show small trees can increase J max , but not V cmax , without additional leaf nitrogen or phosphorus (Figure 1), most likely by increasing nutrient use efficiency (Figure 3). This may occur via a potential re-allocation of nitrogen and phosphorus to optimize photosynthetic capacity (Hasper et al, 2017;Mo et al, 2019). The carboxylation reactions have greater nutrient demand for enzymes, such as RuBisCO, compared to those in the electron transport chain (Evans, 1989;Raven, 2013;Xu et al, 2012).…”

Triose phosphate utilization and beyond: from photosynthesis to end product synthesis

“…Plants grown with different phosphate nutrition are therefore not significantly more or less likely to experience TPU limitation. Most phosphate in photosynthesizing cells will be used in nucleic acids and phospholipids (Dissanayaka et al, 2018), and growth is more sensitive to phosphate nutrition than is photosynthetic rate (Mo et al, 2018). Ellsworth et al (2015) showed that Australian plants growing in the wild with varying phosphate availability were adapted to their environment, and TPU limitation was more likely at high phosphate nutrition.…”

Species‐specific effects of phosphorus addition on tropical tree seedling response to elevated CO2

“…Furthermore, in the P addition treatment there was a marginally significant negative relationship between P affinity and the increase in foliar P concentration between ambient and elevated CO 2 . In a fertilization experiment in lowland tropical China, P addition increased all four functional types of foliar P: structural P, metabolic P, nucleic acid P and residual P of tropical trees (Mo et al, ). The magnitude of change was species‐specific, but species could reallocate P pools to meet photosynthetic demands (Mo et al, ), suggesting that some species may be able to overcome P limitation of certain responses in P‐poor soils.…”

“…In a fertilization experiment in lowland tropical China, P addition increased all four functional types of foliar P: structural P, metabolic P, nucleic acid P and residual P of tropical trees (Mo et al, ). The magnitude of change was species‐specific, but species could reallocate P pools to meet photosynthetic demands (Mo et al, ), suggesting that some species may be able to overcome P limitation of certain responses in P‐poor soils. These results highlight the need for further studies to understand the differences in species PUE or P uptake mechanisms that allow species to thrive in low‐P environments and specifically how they may affect species responses to elevated CO 2 .…”