Variability in growth and biomass allocation and the phenotypic plasticity of seven Prosopis pallida populations in response to water availability

Abstract

Significant changes in root biomass allocation, water transport and leaf structure allow P. pallida seedlings to overcome El Nino extreme events. The North Peruvian dryland forests face long droughts which promote adaptive mechanisms to cope with low water availability. However, the impact of the El Nino South Oscillation on these forests provides a unique set of conditions with high water availability that increase water consumption and plant growth. We studied the performance of seedlings of Prosopis pallida from different populations along an environmental gradient in North Peru. We wanted to know if the responses of growth and biomass allocation to water availability differ among the populations. For this, we grew seedlings from seven P. pallida populations, in a greenhouse experiment, with low or high water availability for 2 months. Our results show that P. pallida responds differently to water availability. Under high water availability, plant biomass was correlated positively to evapotranspiration and root mass allocation, and negatively to leaf mass per area and leaf gas exchange. However, at low water availability, plant biomass was also correlated positively to wood density and negatively to leaf water potential. The relative distance plasticity index showed that the populations responded differently to water availability, but it was not related to climatic factors. Only for a few traits (plant height, instantaneous water use efficiency, and water use efficiency), the phenotypic plasticity was negatively correlated with the mean annual temperature and rainfall at the site of the population´s origin, showing that it was reduced under harsh climatic conditions. In summary, root mass allocation, water transport, and leaf structure play an important role in the growth response of plants of this species to extreme rainfall events.