Different responses of photosynthesis to drought in iso/anisohydric trees

Isohydric and anisohydric behaviors represent distinct stomatal physiological responses of plants to drought, reflecting different strategies to drought stress. However, it remains unclear how stomatal behavior regulate the response of leaf and stem photosynthesis to drought, and how these behaviors influence their interaction. In a greenhouse garden experiment, we applied water control and stem shading treatments on one-year-old seedlings of five tree species (two isohydrics and three anisohydrics) in South China. Leaf water potential, leaf photosynthetic rate, percent loss of conductivity in xylem, relative growth rate and non-structural carbohydrate content were measured to compare the effects of different treatments. Results showed that isohydric seedlings had limited growth under drought, which was exacerbated by stem shading. Anisohydric seedlings had higher xylem embolism under drought, but stem shading did not significantly worsen it, and there was an correlation between stem and leaf photosynthesis. Schima superba, a strongly anisohydric species, upregulated leaf photosynthesis under stem shading to compensate for reduced stem photosynthesis, while another anisohydric specie Syzygium rehderianum showed leaf photosynthesis decreased. This study found that stem photosynthesis could provide an important carbon assimilation supplement when leaf photosynthesis was restricted in drought-stressed isohydric seedlings, and there was an interaction between leaf and stem photosynthesis in anisohydric species, but the direction of correlation was species-specific. Consequently, when conserving species with stronger isohydric behavior under drought conditions, it is essential to pay closer attention to the performance of stem photosynthesis to enhance the survival rate and productivity of these species.