Using physiological and morphological methods for comparison: is mixed Phyllostachys edulis and Carya illinoinensis a reasonable mixed forest model?

Abstract

Abstract The purpose of this study was to investigate whether the Phyllostachys edulis-Carya illinoinensis co-plantation is a feasible forest model. Two treatments and one control were evaluated. The control was a low-density C. illinoinensis forest (CK), and the treatments were a high-density C. illinoinensis forest (DF), and a C. illinoinensis-P. edulis co-plantation forest (MF). Gas exchange and chlorophyll fluorescence parameters, leaf physiology, macromorphology, and anatomical structure of C. illinoinensis were measured and principal component analysis (PCA) was used to evaluate treatment effects. The highest net photosynthetic rate (Pn), which was 13.72 .µmol CO2·m-2·s-1, was recorded for C. illinoinensis under the CK treatment, while the corresponding values for MF and DF treatments were 8.98 and 5.25 µmol CO2·m-2·s-1, respectively. The JIP test revealed that plastoquinone libraries were inhibited under both MF and DF, particularly in the latter. Compared with CK, antioxidant substances in MF and DF leaves increased to a certain extent, again, particularly in the latter. Leaf macromorphology and anatomical structures under the different treatments also changed to acclimated to different environments. The leaf area of MF became lower, and the vascular tissue of DF petiole became larger. Finally, based on the main data, the order of the PCA scores was CK > MF > DF. The results indicated that both co-plantation and high-density planting caused both interspecific and intraspecific competition. Photosynthesis was inhibited in C. illinoinensis to varying degrees under both cultivation models. Nonetheless, the stress levels in C. illinoinensis were significantly lower under the co-plantation forest than under high-density planting. These findings indicate that C. illinoinensis growth was not severely inhibited by co-plantation with P. edulis, as it still developed well. Hence, co-plantation of P. edulis and C. illinoinensis is a promising mixed-forest model.