Carbon allocation, gas exchange, and needle morphology of Pinus ponderosa genotypes known to differ in growth and survival under imposed drought

Abstract

Seedlings from 27 open-pollinated families of ponderosa pine representing nine geographically diverse origins were screened for drought tolerance based on survival and growth under imposed drought. Seedlings that had been preconditioned to drought survived 14 days longer than seedlings that had been well watered before being subjected to drought. Seed sources varied in their ability to survive drought and this variation was accentuated by drought preconditioning. Seedlings from a South Dakota source and a Nebraska source generally survived the longest under drought. Seedlings from a Montana source and a New Mexico source succumbed the fastest after water was withheld. Significant family within source variation in drought survival was observed for some sources. In general, drought survival was poorly correlated to climate indices of the seed sources. Allocation of biomass to roots, stems, and needles varied significantly among the seed sources with the most drought-sensitive sources (Montana and New Mexico) showing the most divergent allocation patterns. The relation between drought survival and shoot/root ratio suggested that there is an optimum pattern of allocation for drought survival. A comparison of the most and least drought-tolerant sources indicated that needle gas exchange (net photosynthesis and needle conductance to water vapor) and predawn needle water potential were similar among the sources regardless of their relative ability to survive drought. Needle morphology traits often associated with variation in drought tolerance, such as stomatal density and specific leaf area, did not differ among the seed sources. However, seedlings from the drought-tolerant sources had shorter needles, less surface area per needle, and fewer stomata per needle than seedlings from the drought-sensitive sources. The results suggest that drought tolerance of ponderosa pine may be improved through seed source selection and, within certain sources, family selection. Allocation patterns and needle morphology appear to play a larger role than needle gas exchange patterns in determining drought tolerance in this species.

Different responses of two contrasting Populus davidiana populations to exogenous abscisic acid application

“…We believe that indeed plants from dry climate population have adapted to tolerate drought by allocation more carbon to roots and maintaining higher WUE, since our results point in the same direction as the earlier studies (Martin and Thorstenson, 1988;Cregg, 1994;Leroux et al, 1996;Schulze et al, 1998;Osorio et al, 1998). Furthermore, our results also showed that changes in WUE were correlated with a large set of parallel changes in plant properties such as Rs and Sla.…”

Drought conditioning improves water status, stomatal conductance and survival ofEucalyptus globulussubsp. bicostataseedlings

“…Survival was inversely correlated with shoot/root biomass ratio. As observed previously a greater allocation to root growth improves seedling survival [8,20]. Midday RWC was also closely correlated with survival, similarly to Mena-Petite et al conclusions [29].…”

“…It has been observed slow growth and changes in dry matter partitioning, mainly reductions in leaf area and shoot/root ratio [22,40]. Stock types with low shoot/root ratio perform better under drought conditions because a more favorable balance between water uptake and loss is reached [8,49]. Physiological changes can include osmotic adjustment, elastic adjustment and stomatal regulation [9,10,40,59].…”

Physiological and growth responses of Populus davidiana ecotypes to different soil water contents

“…WUE seems generally to have a high correlation with plant growth, however, the relationship may be postive or negative. Increasing plant WUE has been shown to either increase or decrease biomass productivity (Cregg, 1994;Leroux et al, 1996;Osorio et al, 1998;Li et al, 2000). When water is limited, plants that use water more efficiency by producing greater biomass for a given quantity of water transpired would grow more rapidly, resulting in a positive correlation between WUE and productivity.…”