Elevated atmospheric CO2 concentration improves water use efficiency and growth of a widespread Cerrado tree species even under soil water deficit

ABSTRACT Changes in atmospheric CO2 levels are accompanied by ecological interactions involving other environmental factors, such as drought, which can severely alter the water balance of plants, thereby influencing sap flow, gas exchange, and plant growth. The objective of this study was to evaluate the water use economy, leaf gas exchange, and growth of young plants of the species Lafoensia pacari subjected to high concentrations of atmospheric CO2 ([CO2]) and soil water deficit. Increased vapor pressure deficit was observed from 1200 to 1800 hours. Plants under elevated [CO2] exhibited increased leaf photosynthesis, resulting in improved growth. Specific leaf area was lower in plants under high [CO2], mainly after soil water deficit treatment. Daily irrigated plants growing under ambient [CO2] had higher stem sap flow velocity (cm h-1) and hourly sap flow (kg h-1), mainly during the hottest hours of the day, than plants under high [CO2]. Improved water use by plants growing under high [CO2] may result in increased availability of water in the soil, partially offsetting future drought events and extending the growth period.

摘要 大气二氧化碳（atmospheric CO2）浓度变化往往伴随涉及其他环境因子的生态交互作用，例如干旱可严重扰乱植物水分平衡，进而影响树液流动（sap flow）、气体交换与植物生长。本研究旨在评估暴露于高大气二氧化碳浓度（[CO2]）与土壤水分亏缺条件下，拉芳西雅帕克瑞（Lafoensia pacari）幼株的水分利用经济性、叶片气体交换特性及生长状况。研究观测到，12:00至18:00时段水汽压亏缺（vapor pressure deficit）升高。高[CO2]处理植株的叶片光合速率提升，生长状况得以改善。高[CO2]处理植株的比叶面积（specific leaf area）更低，该差异在土壤水分亏缺处理后尤为显著。与高[CO2]处理植株相比，本底二氧化碳浓度（ambient [CO2]）下每日灌溉的植株，其茎树液流动速率（cm·h⁻¹）与小时树液流通量（kg·h⁻¹）更高，该差异在当日最热时段尤为突出。高[CO2]环境下植株的水分利用经济性提升，可增加土壤有效水分储量，部分抵消未来干旱事件的影响并延长植物生长周期。