Effects of air warming and soil warming on ecophysiological processes of leaves and fine roots of Cunninghamia lanceolata saplings

Uncertainties about the ecophysiological response of plants to elevated temperature limit our ability to predict the impact of climate change on plants, especially in tropical and subtropical forests. One important source of the uncertainties is that the vast majority of warming studies manipulated only aboveground or only belowground temperature when in the real word warming takes place both aboveground and belowground. We used a full factorial design of air warming and soil warming with four temperature treatments: (1) unwarmed, (2) soil warming, (3) air warming, (4) soil plus air warming to explore the effects of warming on ecophysical processes/characteristics of leaves and fine roots of Chinese-fir saplings. We measured photosynthesis, concentrations of oxidant substances, activity of antioxidant enzymes, and osmoregulatory substances in leaves and fine roots. We found that the soil warming increased photosynthetic rate by 68.9%, but air warming and soil plus air warming treatments did not. The concentrations of oxidant compounds, superoxide anion (O₂^-), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) were higher in leaves than in fine roots under all treatments, possibly due to their differences in the degree of oxidative damage. Soil warming increased leaf catalase (CAT) activity by 58.5%, soil warming and air warming increased leaf peroxidase (POD) activity by 31% and 42.3%, respectively, and soil plus air warming increased leaf ascorbic acid peroxidase (APX) activity by 31%. These increases in antioxidant enzyme concentrations indicated that warming activated leaf antioxidant systems. The CAT activity was lower in leaves than in fine roots, while the POD activity and concentrations of osmoregulatory substances were higher in leaves than in fine roots across all treatments. Our study clearly illustrated that different warming treatments (aboveground and belowground) had different effects on plant growth and physiological processes. The differences in oxidant compounds and activities of antioxidant enzymes between leaves and fine roots indicated that warming affect different organs differently. This study provides insights into how climate warming may affect important physiological and biochemical processes in subtropical forests.