No carbon limitation after lower crown loss in Pinus radiata

Abstract

Background and Aims Biotic and abiotic stressors can cause different defoliation patterns within trees. Foliar pathogens of conifers commonly prefer older needles and infection with defoliation that progresses from the bottom crown to the top. The functional role of the lower crown of trees is a key question to address the impact of defoliation caused by foliar pathogens. Methods A 2 year artificial defoliation experiment was performed using two genotypes of grafted Pinus radiata to investigate the effects of lower-crown defoliation on carbon (C) assimilation and allocation. Grafts received one of the following treatments in consecutive years: control–control, control–defoliated, defoliated–control and defoliated–defoliated. Results No upregulation of photosynthesis either biochemically or through stomatal control was observed in response to defoliation. The root:shoot ratio and leaf mass were not affected by any treatment, suggesting prioritization of crown regrowth following defoliation. In genotype B, defoliation appeared to impose C shortage and caused reduced above-ground growth and sugar storage in roots, while in genotype A, neither growth nor storage was altered. Root C storage in genotype B decreased only transiently and recovered over the second growing season. Conclusions In genotype A, the contribution of the lower crown to the whole-tree C uptake appears to be negligible, presumably conferring resilience to foliar pathogens affecting the lower crown. Our results suggest that there is no C limitation after lower-crown defoliation in P. radiata grafts. Further, our findings imply genotype-specific defoliation tolerance in P. radiata.

Pathogen-induced defoliation impacts on transpiration, leaf gas exchange, and non-structural carbohydrate allocation in eastern white pine (Pinus strobus)

“…In a foliar fungal disease similar to the WPND complex, Douglas-fir (Pseudotsuga menziesii) defoliation via Swiss needle-cast (Phaeocryptopus gaeumannii) was found to significantly reduce wood growth ahead of observed declines in NSC reserves (Saffell et al 2014a, b), suggesting that trees will store NSC in times of defoliation stress to allocate towards new foliar material, maintenance respiration, and defense, at the expense of radial growth. Other studies have demonstrated similar results in which a reduction in wood growth is reported with no change in NSC concentration of defoliated trees, including defoliation of Pinus pinaster by Thaumetopoea pityocampa (Jacquet et al 2013) and repeated artificial defoliation of Pinus radiata genotypes (Gómez-Gallego et al 2020).…”

“…It has been suggested that C allocation priority is first designated to facilitate short-term survival, and then utilized for processes that support long-term fitness (i.e., growth and reproduction), with any excess NSC either actively or passively stored (Dietze et al 2014;Wiley and Helliker 2012). While many studies have investigated NSC allocation and storage within trees subject to either natural (Hudgeons et al 2007;Jacquet et al 2013;Palacio et al 2012;Saffell et al 2014a, b;Wargo et al 2002) or artificial defoliation (Gómez-Gallego et al 2020;Handa et al 2005;Jacquet et al 2014;Li et al 2002;Palacio et al 2008;Puri et al 2015a;Wiley et al 2013Wiley et al , 2016, there is no consistent response that can be assumed to occur for an emerging pathogen complex such as WPND. A subsequent decline or increase of NSC following needle loss is likely a function of defoliation severity, duration, or repetition of the defoliation event, compounded with other abiotic stressors (e.g., drought) and functional traits of the host species.…”

“…In some cases, the time elapsed since the initial defoliation event can influence NSC storage within various tissue pools. Several studies have reported only short-term declines in NSC concentration, with no long-term difference in sugar or starch concentrations between healthy and defoliated trees (Gómez-Gallego et al 2020;Palacio et al 2008Palacio et al , 2012Puri et al 2015b;Saffell et al 2014a, b;Wiley et al 2013). It is plausible that the impacts of WPND have yet to reach a critical threshold of reduced gross carbon assimilation, at which point it may be expected to observe declines in stored NSC.…”

Molecular Phylogenomics and Population Structure of Phytophthora pluvialis

“…However, infected Douglas-fir needles are cast prematurely and severe defoliation in the lower canopy has been noted on occasion in both the US and NZ (Hansen et al 2015). This may suggest a coevolutionary history between the two species whereby P. pluvialis plays a role in the suppression of understory species, a pattern that is characteristic of Douglas-fir stands (Gómez-Gallego et al 2020). This potential coevolution and mutualistic ecological interactions between both species requires further exploration.…”

“…Reports of P. pluvialis in the US are limited to the forests of the PNW (Hansen et al 2015;Gómez-Gallego et al 2020;Brar et al 2018). All of the US samples were collected from a single conifer species, Douglas-fir; whereas the isolates collected in NZ came from four different conifer species.…”