Does root respiration in Australian rainforest tree seedlings acclimate to experimental warming?

Abstract

Plant respiration can acclimate to changing environmental conditions and vary between species as well as biome types, although belowground respiration responses to ongoing climate warming are not well understood. Understanding the thermal acclimation capacity of root respiration (Rroot) in relation to increasing temperatures is therefore critical in elucidating a key uncertainty in plant function in response to warming. However, the degree of temperature acclimation of Rroot in rainforest trees and how root chemical and morphological traits are related to acclimation is unknown. Here we investigated the extent to which respiration of fine roots (≤2 mm) of four tropical and four warm-temperate rainforest tree seedlings differed in response to warmer growth temperatures (control and +6 °C), including temperature sensitivity (Q10) and the degree of acclimation of Rroot. Regardless of biome type, we found no consistent pattern in the short-term temperature responses of Rroot to elevated growth temperature: a significant reduction in the temperature response of Rroot to +6 °C treatment was only observed for a tropical species, Cryptocarya mackinnoniana, whereas the other seven species had either some stimulation or no alteration. Across species, Rroot was positively correlated with root tissue nitrogen concentration (mg g−1), while Q10 was positively correlated with root tissue density (g cm−3). Warming increased root tissue density by 20.8% but did not alter root nitrogen across species. We conclude that thermal acclimation capacity of Rroot to warming is species-specific and suggest that root tissue density is a useful predictor of Rroot and its thermal responses in rainforest tree seedlings.

The physiological acclimation and growth response of Populus trichocarpa to warming

“…R r ,29 values were slightly but not significantly lower and more variable in the warmed treatments than in the ambient treatment; however, those differences were accentuated (becoming marginally significant) when we standardized by root N content ( R r−N ,29 , Table 4 and Figure 5). In agreement with several studies (Ceccon et al 2016; Noh et al 2020; Reich et al 2008), standardizing R r rates by tissue N content helped constrain variation among individuals (Figures S11 and S12) because root tissue N is an important indicator of root metabolic activity due to its involvement with ion uptake, and root protein and enzyme function. Although R r−N ,29 was not different among treatments (Table 4), R r−N at higher temperatures was depressed in the +8°C treatment relative to the two other treatments (Figure 5), pointing to the important role that tissue N content has in relation to R r .…”

“…Using data from eight commonly studied taxa, Smith et al (2019) reported that respiration rates of leaves and photosynthetic stems increased to a greater extent than roots following temperature increase, indicating that leaves and stems have greater thermal acclimation capacity than roots. A second recent study on the respiration rates of tropical seedlings of eight species (Noh et al 2020) found no clear trend in root respiration in response to warming but reported that respiration rates were correlated with root N content, and that the temperature sensitivity of root respiration ( Q 10 R r ) was positively related to root tissue density. Many other studies have confirmed the relationship between root respiration and root tissue N content (Burton et al 2002; Pregitzer et al 1998; Pregitzer et al 2000; Reich et al 2008; Roumet et al 2016).…”

Separating the effects of air and soil temperature on silver birch. Part I. Does soil temperature or resource competition determine the timing of root growth?

“…As soil warming increased root mortality, temperature acclimation of root respiration may not have happened on a large scale during the treatment growing season. The acclimation varies with biomes, tree species, root morphology and soil depths ( Jarvi and Burton 2020 , Noh et al. 2020 ) and seasonal acclimation ( Burton and Pregitzer 2003 ) can be weaker than longer-term acclimation ( Jarvi and Burton 2013 ).…”

Early Growth Responses of Larix kaempferi (Lamb.) Carr. Seedling to Short-Term Extreme Climate Events in Summer

“…In general, moderate warming enhances plant growth due to the increased allocation of carbon to aboveground rather than belowground parts, thereby increasing the shootto-root ratio or total biomass-to-root biomass ratio [66][67][68]. By contrast, drought-induced stress increases the root-to-shoot ratio by increasing the proportion of soluble sugars and starch in roots [16,69,70].…”