Balancing the nutrient needs: Optimizing growth in Malus sieversii seedlings through tailored nitrogen and phosphorus effects

The impact of nitrogen (N) and phosphorus (P) on the physiological and
biochemical processes crucial for tree seedling growth is substantial.
Although the study of plant hydraulic traits in response to N and P is
growing, comprehensive research on their combined effects remains limited.
Malus sieversii, a key ancestral species of modern apples and a dominant
species in Xinjiang's Tianshan wild fruit forest, is witnessing a
decline due to climate change, pests and diseases, compounded by
challenges in seedling regeneration. Addressing this, a four-year study
was conducted to determine the optimal fertilization method for it. The
experiment explored varying levels of N (N10, N20, N40) and P (P2, P4,
P8), and their combined effects (N20Px: N20P2, N20P4, N20P8; NxP4: N10P4,
N20P4, N40P4), assessing their impact on gas exchange, hydraulic traits,
and the interplay among functional traits in Tianshan Mountains' M.
sieversii seedlings. Our study revealed that all nitrogen treatments
enhanced gas exchange, while phosphorus addition negatively impacted it.
N10 significantly increasing leaf hydraulic conductivity. All
phosphorus-inclusive fertilizers adversely affected hydraulic
conductivity. P8, N20P4 and N20P8 notably increased seedlings'
vulnerability to embolism. Seedlings can adaptively adjust multiple
functional traits in response to nutrient changes. The research suggests
N10 and N20 as the most effective fertilization treatments for M.
sieversii seedlings in this region, while fertilization involving
phosphorus is less suitable. This study contributes valuable insights into
the specific nutrient needs of it, vital for conservation and cultivation
efforts in the Tianshan region.