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（CO₂）浓度变化往往伴随涉及其他环境因子的生态交互过程，其中干旱可显著改变植物的水分平衡状态，进而对树液流动、气体交换及植物生长产生影响。本研究旨在评估高大气二氧化碳浓度([CO₂])与土壤水分亏缺处理下，树种Lafoensia pacari幼龄植株的水分利用经济性、叶片气体交换特性及生长表现。研究观测到12:00至18:00时段水汽压亏缺升高。在高[CO₂]环境下生长的植株，其叶片光合速率显著提升，生长状况得以改善。高[CO₂]处理植株的比叶面积更低，该差异在土壤水分亏缺处理后尤为显著。与高[CO₂]环境下的植株相比，常规大气CO₂浓度环境下每日灌溉的植株，其茎液流速率(cm·h⁻¹)与小时液流量(kg·h⁻¹)更高，且该差异主要出现在当日最热时段。高[CO₂]环境下植株的水分利用优化可提升土壤有效水分储量，部分抵消未来干旱事件的影响，并延长植株的生长周期。