Contrasting leaf structural, photosynthetic and allocation responses to elevated [CO2] in different-aged leaves of tropical fruit trees Persea americana and Annona muricata

Responses of leaf photosynthetic traits to elevated growth [CO2] vary among species, but there is limited understanding of underlying trait trade-offs, especially for tropical species with continuous leaf formation. Persea americana and Annona muricata with significant investments in defense structures (idioblasts) were used to study the impacts of growth [CO2] (400 vs 800 μmol mol-1) on leaf structural, chemical, and photosynthetic characteristics at different leaf developmental stages. Growth at elevated [CO2] increased whole plant leaf area (ST) and whole plant average leaf dry mass per unit area (MAv) in P. americana, whereas both ST and MAv were reduced in A. muricata. Elevated [CO2] moderately reduced foliage N and P contents per dry mass in P. americana but increased in A. muricata. In P. americana, elevated [CO2] increased anthocyanin content in young leaves and decreased in mature leaves, and increased the share of idioblast tissue fraction (fI) with moderate downregulation of photosynthesis (A). In A. muricata, elevated [CO2] reduced anthocyanin content in young leaves and fI was unaffected, whereas a major downregulation in A was observed. In this species, photosynthetic downregulation was not associated with nutrient starvation, but occurred due to direct inhibition of stomatal conductance by elevated [CO2], ultimately limiting leaf development and growth and curbing Vcmax and Jmax in mature leaves. These results demonstrate a limited impact of primary/secondary metabolism trade-off on photosynthetic response to growth [CO2], underscore major species differences in response to elevated [CO2] and emphasize the impact of leaf age in determining whole plant growth response.

Pocket gopher disturbance slows soil carbon accumulation in abandoned agricultural lands

Soil carbon (C) sequestration rates vary widely in abandoned agricultural lands, and factors determining this variation, beyond climate, soil type, and productivity, are poorly understood. One such factor is soil disturbance by burrowing mammals. Despite being ubiquitous in all grasslands, the impact of burrowing mammals on soil C dynamics is not well understood. We quantified the major ecosystem processes that are influenced by one such burrowing mammal, plains pocket gophers (Geomys bursarius), in old field ecosystems located in east-central Minnesota, USA. We found pocket gopher abundance varied among old fields, and newly formed gopher mounds covered up to 6% of the soil surface annually. We first measured short-term C pools and fluxes changes induced by gopher activities. Soil N mineralization did not differ between the soil in gopher mounds and undisturbed soil. However, for the soil under gopher mounds, N mineralization was 30% lower as compared to the undisturbed soil. We developed a process model to simulate the long-term gopher disturbance impact on old field soil C accumulation. This simulation showed that pocket gophers reduce both the rate of soil C accumulation and the total C pool. This reduction is primarily driven by reduced plant C input due to the time it requires for the vegetation to recolonize gopher mounds. Soil organic matter (SOM) decomposition changes had only a minor impact. The process model showed that the depth from which burrowing mammals redistribute soil to the surface is a key factor determining the overall impact on SOM. In total, our study indicates that soil disturbance by burrowing animals can significantly reduce C storage in old field ecosystems when the mammals are mostly active in surface soil and can be a significant factor in decreasing overall C sequestration after land abandonment. However, at our study site, gopher abundance decreases with abandonment age, likely cause by successional vegetation changes, thus the gopher disturbance induced reduction in soil C is transient and decreases with abandonment age. This article is protected by copyright. All rights reserved.