Balancing trade-offs: Enhanced carbon assimilation and productivity with reduced nutritional value in a well-watered C4 pasture under a warmer CO2-enriched atmosphere.

The concentration of atmospheric CO2 and temperature are pivotal components of ecosystem productivity, carbon balance, and food security. In this study, we investigated the impacts of a warmer climate (+2 °C above ambient temperature) and an atmosphere enriched with CO2 (600 ppm) on gas exchange, antioxidant enzymatic system, growth, nutritive value, and digestibility of a well-watered, managed pasture of Megathyrsus maximus, a tropical C4 forage grass, under field conditions. Elevated [CO2] (eC) improved photosynthesis and reduced stomatal conductance, resulting in increased water use efficiency and plant C content. Under eC, stem biomass production increased without a corresponding increase in leaf biomass, leading to a smaller leaf/stem ratio. Additionally, eC had negative impacts on forage nutritive value and digestibility. Elevated temperature (eT) increased photosynthetic gains, as well as stem and leaf biomass production. However, it reduced P and K concentration, forage nutritive value, and digestibility. Under the combined conditions of eC and eT (eCeT), eT completely offset the effects of eC on the leaf/stem ratio. However, eT intensified the effects of eC on photosynthesis, leaf C concentration, biomass accumulation, and nutritive value. This resulted in a forage with 12% more acid detergent fiber content and 28% more lignin. Additionally, there was a decrease of 19% in crude protein leading to a 15% decrease in forage digestibility. These changes could potentially affect animal feeding efficiency and feedback climate change, as ruminants may experience an amplification in methane emissions. Our results highlight the critical significance of conducting multifactorial field studies when evaluating plant responses to climate change variables.

Warming and soil water availability affect plant-flower visitor interactions for Stylosanthes capitata, a tropical forage legume.

The reproductive success of a zoophilous plant species depends on biological interaction with pollinators, which involves both the provision and exploitation of flower resources. Currently, there is little information about how future climate change scenarios will impact interactions between plants and their flower visitors in the tropics. This study analyzes the effects of warming and two soil water conditions on interactions between the tropical forage legume species Stylosanthes capitata and its floral visitors during the flowering period. We used a temperature-free air-controlled enhancement (T-FACE) facility to simulate future warming scenarios by increasing canopy temperature. The tested treatments were: irrigated and ambient canopy temperature (Control); non-irrigated and ambient canopy temperature (wS); irrigated and elevated canopy temperature (eT, +2 °C above ambient canopy temperature); and non-irrigated and elevated canopy temperature (wSeT). The effects of treatments on the time of flower opening and closing, sugar concentration in the nectar, and plant-flower visitor interactions were assessed. In the warmed treatments, S. capitata flower opening occurred ~45 min earlier compared to non-warmed treatments, and flowers remained opened for only ~3 h. Further, the sugar concentration in the nectar from eT was 39% higher than in the Control. The effects of warming on floral biology and flower resource production in S. capitata had an impact on the plant-floral visitor relationships with the bees Apis mellifera and Paratrigona lineata, the most abundant potential pollinating floral visitors, and the butterfly visitor Hemiargus hanno. Additionally, around noon, the interactive and additive effects of the combined wS and eT treatments decreased insect visiting frequency. These results suggest that warming and soil water deficiency could affect flower-visitor interactions and thus the reproductive success of S. capitata in tropical belts.

Depicting the mating system and patterns of contemporary pollen flow in trees of the genus Anadenanthera (Fabaceae).

Anadenanthera (Fabaceae) is endemic to the Neotropics and consists of two tree species: A. colubrina (Vell.) Brenan and A. peregrina (L.) Speg. This study examined the mating system and contemporary gene flow of A. colubrina (Acol) and A. peregrina (Aper) in a highly fragmented area of the Atlantic Forest to provide valuable information that informs conservation strategies. Reproductive adults from forest remnants [n A. colubrina = 30 (2.7 ha), n A. peregrina = 55 (4.0 ha)] and progeny-arrays (n A. colubrina = 322, n A. peregrina = 300) were genotyped for seven nuclear microsatellite markers. Mating system analyses revealed that A. colubrina is a mixed mating species (tm = 0.619) while A. peregrina is a predominantly outcrossing species (tm = 0.905). For both Anadenanthera species, high indices of biparental inbreeding were observed (Acol = 0.159, Aper = 0.216), resulting in low effective pollination neighborhood sizes. Categorical paternity analysis revealed different scales of pollen dispersal distance: the majority of crossings occurring locally (i.e., between nearby trees within the same population), with moderate pollen dispersal coming from outside the forest fragments boundaries (Acol mp = 30%, Aper mp = 35%). Nevertheless, pollen immigration from trees outside the populations for both species suggests that the populations are not reproductively isolated. This study highlights the importance of evaluating both mating system and contemporary gene flow for a better understanding of the biology of Anadenanthera species. This information should be considered to ensure the effective conservation and management practices of these plant species.

Warming and elevated CO2 induces changes in the reproductive dynamics of a tropical plant species.

Tropical plant species are vulnerable to climate change and global warming. Since flowering is a critical factor for plant reproduction and seed-set, warming and elevated atmospheric carbon dioxide concentrations (eCO2) are crucial climate change factors that can affect plant reproductive dynamics and flowering related events in the tropics. Using a combined free-air CO2 enrichment and a free-air temperature-controlled enhancement system, we investigate how warming (+2 °C above ambient, eT) and elevated [CO2] (~600 ppm, eCO2) affect the phenological pattern, plant-insect interactions, and outcrossing rates in the tropical legume forage species Stylosanthes capitata Vogel (Fabaceae). In comparison to the control, a significantly greater number of flowers (NF) per plot (+62%) were observed in eT. Furthermore, in warmed plots flowers began opening approximately 1 h earlier (~09:05), with a canopy temperature of ~23 °C, than the control (~09:59) and eCO2 (~09:55) treatments. Flower closure occurred about 3 h later in eT (~11:57) and control (~13:13), with a canopy temperature of ~27 °C. These changes in flower phenology increased the availability of floral resources and attractiveness for pollinators such as Apis mellifera L. and visitors such as Paratrigona lineata L., with significant interactions between eT treatments and insect visitation per hour/day, especially between 09:00-10:40. In comparison to the control, the additive effects of combined eCO2 + eT enhanced the NF by 137%, while the number of A. mellifera floral visits per plot/week increased by 83% during the period of greatest flower production. Although we found no significant effect of treatments on mating system parameters, the overall mean multilocus outcrossing rate (tm = 0.53 ± 0.03) did confirm that S. capitata has a mixed mating system. The effects of elevated [CO2] and warming on plant-pollinator relationships observed here may have important implications for seed production of tropical forage species in future climate scenarios.