Tomato Rootstocks Mediate Plant-Water Relations and Leaf Nutrient Profiles of a Common Scion Under Suboptimal Soil Temperatures

Abstract

Environments with short growing seasons and variable climates can have soil temperatures that are suboptimal for chilling-sensitive crops. These conditions can adversely affect root growth and physiological performance thus impairing water and nutrient uptake. Four greenhouse trials and a field study were conducted to investigate if rootstocks can enhance tomato performance under suboptimal soil temperatures (SST). In a controlled greenhouse environment, we exposed four commercial rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) grafted with a common scion (cv. BHN-589) to optimal (mean: 24°C) and SST (mean: 13.5°C) and compared their performance with the non-grafted BHN-589 cultivar. Several root and shoot physiological traits were evaluated: root hydraulic conductivity and conductance, root anatomy, leaf gas exchange, leaf δ¹³C, shoot C and N, and biomass. Under field conditions, the same five phenotypes were evaluated for canopy growth, normalized difference vegetation index (NDVI), leaf nutrients, biomass, and yield. Under SST, root hydraulic conductivity (Lp) and conductance (K _R), stomatal conductance (g _s), and plant biomass decreased. Hydrostatic Lp decreased more than osmotic Lp (Lp ^∗ _hyd: 39-65%; Lp ^∗ _os: 14-40%) and some of the reduced conductivity was explained by the increased cortex area of primary roots observed under SST (67-140%). Under optimal soil temperatures, all rootstocks conferred higher g _s than the non-grafted cultivar, but only two rootstocks maintained higher g _s under SST. All phenotypes showed greater reductions in shoot biomass than root biomass resulting in greater (∼20%) root-to-shoot ratios. In the field, most grafted phenotypes increased early canopy cover, NDVI, shoot biomass, and fruit yield. Greenhouse results showed that Lp ^∗ _os may be less affected by SST than Lp ^∗ _hyd and that reductions in Lp may be offset by enhanced root-to-shoot ratios. We show that some commercial rootstocks possess traits that maintained better rates of stomatal conductance and shoot N content, which can contribute toward better plant establishment and improved performance under SST.

Keywords: Solanum lycopresicum L; grafting; mineral nutrition; root anatomy; root hydraulic conductivity; stomatal conductance.

FIGURE 1

Root hydrostatic (Lp*_hyd; A) and osmotic (Lp*_os; B) hydraulic conductivity on whole-root systems of four grafted rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) and one cultivar (BHN-589) grown under optimal (gray) and suboptimal (white) soil temperatures for 4 weeks. All rootstocks were grafted with BHN-589. Values are mean ± standard error (A: n = 25–31; B: n = 23–31). Means followed by different letters are statistically different at P < 0.01.

FIGURE 2

Root hydrostatic (K_R–hyd; A) and osmotic (K_R–os; B) hydraulic conductance on whole-root systems of four grafted rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) and one cultivar (BHN-589) grown under optimal (gray) and suboptimal (white) soil temperatures for 4 weeks. All rootstocks were grafted with BHN-589. Values are mean ± standard error (A: n = 28–34; B: n = 24–29). Means followed by different letters are statistically different at P < 0.01.

FIGURE 3

Stomatal conductance (g_s; A), and photosynthetic rate (P_n; B) of four grafted rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) and one cultivar (BHN-589) grown under optimal (gray) and suboptimal (white) soil temperatures for 4 weeks. All rootstocks were grafted with BHN-589. Values are mean ± standard error (A: n = 14 and 48 total measurements; B: n = 6 and 24 total measurements) Means followed by different letters are statistically different at P < 0.01.

FIGURE 4

Total biomass (root + shoot; A), root-to-shoot ratio (B), and C-to-N ratio (C) of four grafted rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) and one cultivar (BHN-589) grown under optimal (gray) and suboptimal (white) soil temperatures for 4 weeks. All rootstocks were grafted with BHN-589. Values are mean ± standard error (A,B: n = 45–50; C: n = 10). Means followed by different letters are statistically different at P < 0.01.

FIGURE 5

Changes in canopy cover of four grafted rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) and one cultivar (BHN-589) grown under field conditions. All rootstocks were grafted with BHN-589. All canopies were measured at 8, 22, 29, 36, and 44 days after planting (x-values staggered for visual clarity). Canopy cover values were inverse-negative-log transformed prior to slope comparisons. Data presented is untransformed. Points are mean ± standard error (n = 7–8). Legend information followed by different letters are mean-slopes statistically different at P < 0.05.

FIGURE 6

Shoot dry biomass (A), and total fresh fruit (B) of four grafted rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) and one cultivar (BHN-589) grown under field conditions. All rootstocks were grafted with BHN-589. Values are mean ± standard error (A,B: n = 8). Means followed by different letters are statistically different at P < 0.05.

FIGURE 7

Linear discriminant analysis based on ten nutrients (B, Ca, Cu, Fe, K, Mg, Mn, Na, P, Zn) at 3 times points (26, 62, 126 DAP) and C and N at 126 DAP for four grafted phenotypes (Estamino, Maxifort, RST-04-106-T, and Supernatural) and one cultivar (BHN-589) (n = 8). Total variance explained by the first two discriminant functions are presented in parentheses.