Xylem cavitation for black cottonwood and 10 native and invasive tree species in North America

Three experiments were conducted to investigate topics related to xylem cavitation for trees: (1) How trees deal with cavitation diurnally; (2) how stomatal behavior affects the occurrence of cavitation; and (3) how resistance to cavitation differs between native and invasive trees. In the first experiment, we studied cavitation repair for two genotypes of black cottonwood exhibiting divergent stomatal behavior under water stress: one genotype incompletely closes its stomata (ISC genotype) while the other genotype closes its stomata (SC genotype). For plants grown in a greenhouse, cavitation repair occurred when xylem water potential was ≥-0.20 MPa and did not occur at values below -0.20 MPa. Refilling was observed only for the ISC genotype, apparently because Psix's were <-0.20 MPa for the SC genotype. Cavitation repair did not occur for plants grown in field plots, where water potentials at predawn were <-0.30 MPa.;In the second experiment, using the same genotypes of black cottonwood, greater cavitation was displayed for the ISC genotype compared to the SC genotype during severe water stress, which appeared to be due to incomplete stomatal closure. Cavitation and transpiration were not different between the two genotypes under well-watered and mild water stress conditions. Cavitation (acoustic emissions) and transpiration were not correlated, suggesting a complex relationship between the two variables.;In the third experiment, we tested the hypothesis that invasive trees have hydraulic advantages compared to co-occurring native trees. We compared resistance to drought-induced xylem cavitation and xylem specific hydraulic conductivity between co-occurring native and invasive species pairs, hypothesizing that both measures would be greater for invasives. Five pairs of co-occurring invasive and native trees were selected, as follows: (1) Tamarisk ramosissima and Salix amygdaloides; (2) Robinia pseudoacacia and Alnus rhombifolia; (3) Schinus terebinthifolius and Myrica cerifera; (4) Ligustrum sinense and Acer negundo; and (5) Sapium sebiferum and Diospyros virginiana. Native and invasive trees showed no difference in their resistance to cavitation. Xylem specific conductivity showed no difference for any of the co-occurring species pairs. Apparently, invasive trees do not display consistent hydraulic advantages compared to native trees.