Autumnal Potassium Induced Modulations in Plant Osmoprotectant Substances, Nutrient Stoichiometry and Precision Sustainable Seedling Cultivation in Parashorea chinensis

Abstract

Parashorea chinensis, an endemic tree species in China’s tropical rainforests, holds ecological and economic importance. Challenges like low resistance, poor quality, and low survival rates hinder its successful cultivation. This study explores the potential of autumn potassium fertilization on Parashorea seedlings from two provenances (Napo and Tianyang). The treatments included no fertilizer (CK-1), a single application of 160 mg K·plant−1 (CK-2), and various potassium levels K1, K2, K3, K4, K5, and K6 (corresponding to 0, 40, 80, 160, 320, and 640 mg·K·plant−1, respectively) combined with nitrogen (200 mg·plant−1) and phosphorus (80 mg·plant−1) fertilization. The findings indicate that autumn potassium application, in conjunction with nitrogen (N) and phosphorus (P) fertilization, significantly enhances seedling height and biomass in both provenances, resulting in an average increase of 101% and 89% under the K4 treatment compared to CK-1 and CK-2, comparatively. Both Napo and Tianyang provenances exhibited distinct responses in photosynthetic rate (2.70 μmol·m−2·s−1 and 1.97 μmol·m−2·s−1, respectively) and stomatal conductance (0.042 mol·m−2·s−1 and 0.029 mol·m−2·s−1, respectively) to the K4 treatment, which proved most effective. The chlorophyll content was significantly higher for Napo provenance with the K3 treatment (74.31%, 58.99%), while for Tianyang, it was higher with the K4 treatment (41.48%, 17.36%), compared to CK-1 and CK-2, respectively. Antioxidant enzymes activity, osmoregulatory capacity, and malondialdehyde content all exhibited variations with potassium application levels, with the K4 treatment offering significant benefits. In Napo provenance, lignin (199.82 mg·g−1) and cellulose (252.38 mg·g−1) peaked at K4, while Tianyang exhibited variation, higher lignin (184.25 mg·g−1) at K3, and cellulose (257.73 mg·g−1) at K4. Nutrient content analysis demonstrates that the K4 treatment enhances nutrient absorption and storage, increasing total N (21.56 mg·kg−1), P (4.69 mg·kg−1), and K (13.49 mg·kg−1) content. A comprehensive analysis reveals that the K4 treatment yields the highest quality scores (1.87, 1.85) and membership values (0.82, 0.68) for both Napo and Tianyang seedlings, with Napo seedlings outperforming their Tianyang provenance. Thus, treatment K4 underscores the effectiveness of autumn potassium applications for robust seedling cultivation and adaptation, offering valuable insights for sustainable cultivation practices.