Interactions between seedlings of the invasive tree <i>Ailanthus altissima</i> and the native tree <i>Robinia pseudoacacia</i> under low nutrient conditions

<div><p>The allelopathic effect of <i>A. altissima</i> and the nitrogen fixing ability of <i>R. pseudoacacia</i> make the interaction between these two species important to community dynamics. A replacement series greenhouse experiment was used to investigate the type of interaction between seedlings of <i>A. altissima</i> and <i>R. pseudoacacia</i> at high and low soil nutrition states<i>.</i> Also, seeds of <i>A. altissima</i> from its native (China) and invasive ranges (USA) were used to compare the effect of the different seed sources on the interaction with <i>R. pseudoacacia. Robinia pseudoacacia</i> was the better competitor. The presence of <i>A. altissima</i> significantly inhibited nodulation of <i>R. pseudoacacia</i> roots. In summary, in low nutrient early succession sites, seedlings of <i>R. pseudoacacia</i> and <i>A. altissima</i> will coexist and <i>R. pseudoacacia</i> will be the better competitor. However, <i>A. altissima</i> can increase its competitive ability by inhibiting nitrogen fixation by <i>R. pseudoacacia</i>. Differences between the competitive ability of the Chinese and US seed lots of <i>A. altissima</i> did not support the rapid evolution theory for invasive species success.</p></div

A Rootstock Provides Water Conservation for a Grafted Commercial Tomato (<i>Solanum lycopersicum</i> L.) Line in Response to Mild-Drought Conditions: A Focus on Vegetative Growth and Photosynthetic Parameters

<div><p>The development of water stress resistant lines of commercial tomato by breeding or genetic engineering is possible, but will take considerable time before commercial varieties are available for production. However, grafting commercial tomato lines on drought resistant rootstock may produce drought tolerant commercial tomato lines much more rapidly. Due to changing climates and the need for commercial production of vegetables in low quality fields there is an urgent need for stress tolerant commercial lines of vegetables such as tomato. In previous observations we identified a scion root stock combination (‘BHN 602’ scion grafted onto ‘Jjak Kkung’ rootstock hereafter identified as 602/Jjak) that had a qualitative drought-tolerance phenotype when compared to the non-grafted line. Based on this initial observation, we studied photosynthesis and vegetative above-ground growth during mild-drought for the 602/Jjak compared with another scion-rootstock combination (‘BHN 602’ scion grafted onto ‘Cheong Gang’ rootstock hereafter identified as 602/Cheong) and a non-grafted control. Overall above ground vegetative growth was significantly lower for 602/Jjak in comparison to the other plant lines. Moreover, water potential reduction in response to mild drought was significantly less for 602/Jjak, yet stomatal conductance of all plant-lines were equally inhibited by mild-drought. Light saturated photosynthesis of 602/Jjak was less affected by low water potential than the other two lines as was the % reduction in mesophyll conductance. Therefore, the Jjak Kkung rootstock caused aboveground growth reduction, water conservation and increased photosynthetic tolerance of mild drought. These data show that different rootstocks can change the photosynthetic responses to drought of a high yielding, commercial tomato line. Also, this rapid discovery of one scion-rootstock combination that provided mild-drought tolerance suggests that screening more scion-rootstock combination for stress tolerance may rapidly yield commercially viable, stress tolerant lines of tomato.</p></div

The total number of mature leaves (A, B, C) and the total plant length (D, E, F) for three different lines of tomato grown with daily watering (control) or daily watering until water was withheld between day 20 and day 28 (mild-drought treatment).

<p>602 = ‘BHN 602’; 602/Cheong  =  refers to line ‘BHN 602’ scion grafted onto ‘Cheong Gang’ rootstock; 602/Jjak refers to line ‘BHN 602’ scion grafted onto ‘Jjak Kkung’ rootstock. Error bars represent two standard errors on each side of the mean. *  =  significant difference between control and mild-drought treated plants within a plant type (Student's t-test; p<0.05). δ  =  significant difference between 602/Jjak control plants and 602 control plants (Student's t-test; p<0.05).</p

Mean midday light saturated net photosynthesis (A, B, C) and CO₂ saturated net photosynthesis (D, E. F) for three lines of tomato grown with daily watering (filled bars) or daily watering until water was withheld between day 20 and day 28 (open bars).

<p>602 = ‘BHN 602’; 602/Cheong  =  ‘BHN 602’ scion grafted onto ‘Cheong Gang’ rootstock; 602/Jjak  =  ‘BHN 602’ scion grafted onto ‘Jjak Kkung’ rootstock. Error bars represent two standard errors on each side of the mean. *  =  significant difference between control and mild-drought treated plants within a plant type (Student's t-test; p<0.05).</p

The relationship between growth rate (dry weight gain per day) and total stem length is plotted for three different lines of tomato for mild-drought treated and control plants.

<p>602 = ‘BHN 602’; 602/Cheong  =  refers to line ‘BHN 602’ scion grafted onto ‘Cheong Gang' rootstock; 602/Jjak refers to line ‘BHN 602’ scion grafted onto ‘Jjak Kkung’ rootstock. Dashed lines represent first order regressions for all data below 200 cm length. Solid lines refer to second order regressions for all data.</p

Results for 2-way ANOVA performed on total plant length at each sample date.

<p>The effects of plant line, dry treatment and their interaction were tested. Degrees of freedom were: Drought treatment  = 1, Plant line  = 2; dry treatment x plant line interaction  = 2, residuals  = 51, Total = 56. Bold values are significant at the 0.05 level.</p><p>Results for 2-way ANOVA performed on total plant length at each sample date.</p

The Relative growth rates (RGR) for three lines of tomato experiencing either control conditions or a mild-drought are shown.

<p>Relative growth rate was calculated for each plant line either before or after the drought treatment was initiated. Student's t-Tests are presented for the comparison between the RGR of plants experiencing control or mild-drought treatments either before or after the mild-drought was initiated. Also, Student's t-Tests are presented for the comparison between before and after mild-drought was initiated for both control and mild-drought treatment groups. Significant difference between groups is indicated as a bold face P value. 602 = BHN 602 non-grafted; 602/Cheong = BHN 602 scion grafted onto ‘Cheong Gang’ root stock; 602/Jjak  =  BHN 602 scion grafted onto ‘Jjak Kkung’ root stock.</p><p>The Relative growth rates (RGR) for three lines of tomato experiencing either control conditions or a mild-drought are shown.</p

The microclimatic conditions at canopy height in the growth room used for an experiment on grafted and non-grafted lines of tomato are shown.

<p>A) Six representative diurnal cycles of air temperature and relative humidity; B) Six representative diurnal cycles of photosynthetic photon flux density (PPFD); C) Daily maximum and minimum air temperature and relative humidity over the 30 day experimental period.</p

Mean midday water potential (A, B, C) and midday stomatal conductance (D, E, F) for three different lines of tomato grown with daily watering (control) or daily watering until water was withheld between day 20 and day 28 (mild-drought treatment).

<p>602 = ‘BHN 602’; 602/Cheong  =  refers to line ‘BHN 602’ scion grafted onto ‘Cheong Gang’ rootstock; 602/Jjak refers to line ‘BHN 602’ scion grafted onto ‘Jjak Kkung’ rootstock. Error bars represent two standard errors on each side of the mean. *  =  significant difference between control and mild-drought treated plants within a plant type (Student's t-test; p<0.05).</p

Comparison between three lines of tomato plants treated with either mild-drought or no-drought (control).

<p>Student's t-Test assuming unequal variance was used to test for significant differences between mild-drought and control groups for each plant line. P values for two-tailed results are shown. Bold p values indicate significant difference between mild drought and control treatment plants. Significant difference is assigned at the p< = 0.05 level. 602 = BHN 602 non-grafted; 602/Cheong  =  BHN 602 scion grafted onto ‘Cheong Gang’ root stock; 602/Jjak  =  BHN 602 scion grafted onto ‘Jjak Kkung’ root stock.</p><p>Comparison between three lines of tomato plants treated with either mild-drought or no-drought (control).</p