[Effects of nitrogen and phosphorus addition on leaf thermal tolerance in different provenances of Quercus variabilis].

To explore potential effects of soil nutrient on leaf thermal tolerance across geographical origins, five provenance, i.e., Chengbu of Hunan (CB), Zigui of Hubei (ZG), Neixiang of Henan (NX), Lincheng of Heibei (LC) and Pinggu of Beijing (PG), seedlings of Quercus variabilis were cultivated under nitrogen and phosphorus addition. Leaf thermal tolerance parameters (cold, heat and span), nutrient concentrations (nitrogen and phosphorus), nitrogen use efficiency (NUE) and phosphorus use efficiency (PUE), as well as non-structural carbohydrate (soluble sugar and starch) concentrations were analyzed. The results were shown as follows: Nutrient absorption and utilization efficiency varied between oak origins with no obvious geographical trends. PG had higher nutrient use efficiency (NUE and PUE), whereas NX had lower PUE under all treatments. CB had the highest PUE under phosphorus addition. Compared with the control, nutrient addition increased the cold tolerance of PG and LC, and to some extent, increased the heat tolerance of the three middle provenances (ZG, NX, LC). However, the thermal span was opposite to the cold tolerance, as nutrient addition decreased the thermal span of PG and LC but increased that of NX. The leaf cold tolerance had significantly positive correlation with soluble sugar concentration, while the heat tolerance negatively and positively correlated with leaf phosphorus and ratio of nitrogen to phosphorus, respectively. No significant correlation was found between leaf thermal span and leaf chemical substances. To sum up, nutrient use efficiency varying in provenances might be contributed by the original habitats and consequently presented with some local adaptation characteristics, which complicated the response of thermal tolerance to nutrient addition.