Dry weight partitioning and hydraulic traits in young Pinus taeda trees fertilized with nitrogen and phosphorus in a subtropical area

FAUSTINO L, BULFE N, PINAZO M, MONTEOLIVA S, GRACIANO C

TREE PHYSIOLOGY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2013 vol. 33 p. 241 - 251

0829-318X

Plants of Pinus taeda that belong to four families were fertilized with N, P or both nutrients at planting. Two families (H and IH) were the families with highest growth rate while the other two families (IL and L) were the families with lower growth rate of the genetic breeding program. Measurements to evaluate some aspects of the hydraulic architecture of the plants were done during the first year after planting. Stomatal conductance (gs), water potential at midday (Ψmidday), photosynthetic rate at light saturation (Asat), xylem water conductivity of branches (Ks and Kl>) and resistance to water movement of branches with needles (R) were measured. One year after planting, dry mass partitioning of all aboveground organs was measured. P-fertilization increased growth in the four families, while N-fertilization had a depressive effect in growth. L family was more negative affected than H family. The depressive effect is not due to problems in N or P uptake, because plants of all families and treatments had the same N and P concentration in needles. P-fertilization mostly did not change hydraulic parameters. The depressive effect of N can be explained by some changes in hydraulics traits. In L family, the natural high amount of needles per branch was exacerbated by N-fertilization. This change, together with high resistance of branches to water movement, decreases the delivery of water to needles. Therefore reduction in gs was not enough to avoid the drop in Ψmidday. Consequently, stomatal closure and the deficient water status in needles ended in reduction of growth, although Asat was not affected. On H family, the increase of needles per branch due to N-fertilization was counteracted by a reduction in gs but also a reduction of tracheid lumen, in a way that the higher tension in the xylem probably did not induce embolism in the xylem. Because of these two changes, Ψmidday did not drop and water status in needles was good and growth could be sustained. In conclusion, fertilization affects hydraulic architecture of plants and some of those changes can explain the depressive effect of fertilization with N. Moreover, different families develop different strategies.