Warming and water deficit impact leaf photosynthesis and decrease forage quality and digestibility of a C4 tropical grass

Abstract

Global warming is predicted to cause more intense extreme events such as heat waves, flooding and severe droughts, producing significant effects on agriculture. In tropics, climate change will severely impact livestock production affecting water availability, forage quality and food for cattle. We investigated the isolated and combined effects of soil water deficit (wS) and + 2°C increase in canopy temperature (eT) on leaf gas exchange, chlorophyll fluorescence, carbohydrate content, forage quality and in vitro dry matter digestibility (IVDMD) of a field‐grown C4 tropical forage grass Panicum maximum Jacq. using a temperature‐free air‐controlled enhancement (T‐FACE) system. The wS and eT treatments showed no effects on photosystem II photochemistry. However, wS under ambient temperature decreased net photosynthesis rate (A), stomatal conductance (gs) and maximum rate of carboxylation of Rubisco (Vcmax), leading to a reduced starch content in leaves. A 16% reduction in leaf dry mass (LDM) and reduction in forage quality by increasing fibers, reducing crude protein (CP) and decreasing the IVDMD was also observed by effect of wS. Warming under adequate soil moisture (eT) significantly increased LDM by 25% but reduced the forage quality, increasing the lignin content and reducing starch, CP and digestibility. The combined wSeT treatment reduced A, gs, Vcmax and the forage quality. When compared to control, the lignin content in leaves increased by 43, 28 and 17% in wS, eT and wSeT, respectively, causing a significant reduction in IVDMD. We concluded that despite physiological mechanisms to acclimate to warming, both warming and water deficit will impair the quality and digestibility of C4 tropical pastures.

Effect of Long-Term Experimental Warming on the Nutritional Quality of Alpine Meadows in the Northern Tibet

“…The content of CP, ADF (16.26%-55.39%), NDF, EE (2.48%-4.38%), Ash (7.89%-21.95%) and WSC (3.08%-6.76%) in this study were equivalent to the results (CP: 2.71%-19.21%; ADF: 9.06%-48.30%; NDF: 12.16%-76.23%; EE: 0.64%-10.90%; Ash: 3.49%-12.47%; WSC: 1.24%-17.27%) observed in alpine meadows on the Tibetan Plateau by previous studies (Xu et al, 2002;Shi et al, 2013;Sun et al, 2015;Zhang et al, 2015b;Fan et al, 2017;Li and Liu, 2017;Zhang et al, 2017;Li et al, 2018). Increased water availability may have increased the content of CP in this study, which was in line with the results observed in the steppes of Inner Mongolia Autonomous Region, China (Schönbach et al, 2012;Ren et al, 2016a), a C4 tropical grass in Brazil (Habermann et al, 2019), mountain side grasslands in North-West Greece (Roukos et al, 2011) and alpine meadows on the Tibetan Plateau (Yao et al, 2019). This finding may be related to several mechanisms.…”

“…First, increased water availability may accelerate soil nitrogen mineralization and in turn increase the availability of nitrogen to plants (Austin et al, 2004;Miao et al, 2015). Second, increased water availability may increase the capacity of plants to assimilate nitrogen by affecting the activities of nitrogen anabolism, net photosynthetic rate and/or stomatal conductance (Xu and Zhou, 2006;Habermann et al, 2019). Third, increased water availability may promote new tissues generation and delay the maturation of the plants (Schönbach et al, 2012;Ren et al, 2016a).…”

Elevated CO2 and warming change the nutrient status and use efficiency of Panicum maximum Jacq

“…Experiments suggest that Panicum maximum (Guinea grass) would benefit by a 2˚C warming under well-watered conditions by exhibiting increased dry mass [11] and not showing increased concentration of stress indicators compounds, such as malondialdehyde and hydrogen peroxide [12]. However, under heating, there was no increase in photosynthesis and transpiration [6,13], suggesting that under a warmed atmosphere, P. maximum may exhibit increased NUE. It was also observed that under heating, P. maximum exhibited an increase in the concentration of many amino acids, such as valine, threonine and phenylalanine, which have N in their structure [14].…”

Embedded Deforestation: The Case Study of the Brazilian–Italian Bovine Leather Trade

“…Besides legal and reputational risks, the leather supply chain can also be exposed to operational risk. Increased deforestation, the feedback loop of climate change, water shortage and altered rainfall patterns is affecting the availability of resources for all industries, including cattle farming in Brazil [52,53]. and 6404) in 2018, in trade value (million USD).…”