Effects of Organic Polymer Compound Material on K+ and Na+ Distribution and Physiological Characteristics of Cotton Under Saline and Alkaline Stresses

Soil salinization and alkalization greatly restrict crop growth and yield. In this study, NaCl (8 g kg−1) and Na2CO3 (8 g kg−1) were used to create saline stress and alkaline stress on cotton in pot cultivation in the field, and organic polymer compound material (OPCM) and stem girdling were applied before cotton sowing and at flowering and boll-forming stage, respectively, aiming to determine the effects of OPCM on K+ and Na+ absorption and transport and physiological characteristics of cotton leaf and root. The results showed that after applying the OPCM, the Na+ content in leaf of cotton under saline stress and alkaline stress were decreased by 7.72 and 6.49%, respectively, the K+/Na+ ratio in leaf were increased by 5.65 and 19.10%, respectively, the Na+ content in root were decreased by 9.57 and 0.53%, respectively, the K+/Na+ ratio in root were increased by 65.77 and 55.84%, respectively, and the transport coefficients of K+ and Na+ from leaf to root were increased by 39.59 and 21.38%, respectively. The activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and the relative electrical conductivity (REC) in cotton leaf were significantly increased, while the content of malondialdehyde (MDA) was decreased; but the changes in those in root were not significant. The boll weights were increased by 11.40 and 13.37%, respectively, compared with those for the control. After stem girdling, the application of OPCM still promoted the ion transport of cotton organs; moreover, the CAT activity in root was increased by 25.09% under saline stress, and the SOD activity in leaf and CAT in root were increased by 42.22 and 6.91%, respectively under alkaline stress. Therefore, OPCM can significantly change the transport of K+ and Na+ to maintain the K+ and Na+ homeostasis in leaf and root, and regulate physiological and biochemical indicators to alleviate the stress-induced damage. Besides, the regulation effect of OPCM on saline stress was better than that on alkaline stress.

The size and the age of the metabolically active carbon in tree roots

Little is known about the sources and age of C respired from tree roots. Previous research in tree stems has identified two functional pools of non-structural carbohydrates (NSC): an ‘active’ pool supplied directly from canopy photo-assimilates that supports metabolism and a ‘stored’ pool used when fresh C supplies are limited. We compared the C isotope composition of water soluble NSC and respired CO for aspen roots (Populus tremula hybrids) that were cut off fresh C supply via stem-girdling and prolonged incubation of excised roots. We used bomb radiocarbon to estimate the time elapsed since C fixation for respired CO, water-soluble C, and structural α-cellulose. While freshly excised roots respired CO with mean age <1 yr, within a week the age increased to 1.6-2.9 yr. Freshly excised roots from trees girdled ~3 months previously had similar respiration rates and NSC stocks as un-girdled trees, but respired older C (~1.2 yr). We estimate the NSC in girdled roots must be replaced 5-7 times by reserves remobilized from root-external sources. Using a mixing model and observed correlations between ΔC of water-soluble C and α-cellulose, we estimate ~30% of C is ‘active’ (~5 mg C g).

Modeling FoRTE, the Forest Resilience Threshold Experiment

&lt;p&gt;Forested ecosystems represent a large yet uncertain fraction of the global terrestrial carbon sink. Their future state depends on a number of natural and anthropogenic influences; a particularly large uncertainty is how disturbance affects vegetation structure and ecosystem biogeochemistry.&amp;#160;&amp;#160;We used the Ecosystem Demography model to explore the ecological and biogeochemical consequences of disturbance as part of the Forest Resilience Threshold Experiment (FoRTE), a dual modeling and manipulative field experiment investigating the effects of disturbance at different severities on a century-old deciduous forest. The field component was conducted at the University of Michigan Biological Station (UMBS), where stem girdling was applied to achieve four different severity levels of disturbance (0, 45, 65, and 85% gross defoliation) before the 2019 growing season. Since then, we have tracked the subsequent changes in vegetation and biogeochemistry. The modeling component attempted to simulate the FoRTE disturbance treatments within its framework. While we were able to instantiate a forest in ED with a similar climatology, soil characteristics, disturbance history, and vegetation of UMBS,&amp;#160; baseline ED is ultimately unable to reproduce the vegetation dynamics and carbon fluxes observed at the UMBS control plots. This is consistent with previous work where the model is not capable of matching observed carbon and vegetation dynamics. However, ED&amp;#8217;s response to the disturbance treatments is consistent with observations from UMBS: in both the model and UMBS experimental results, we observed different resiliences and carbon cycle responses with respect to disturbance severity. These intriguing results point to both weaknesses and new possibilities in the modeling of ecosystems facing rising disturbances and climate change.&lt;/p&gt;

Phenology and Dispersal of the Wheat Stem Sawfly (Hymenoptera: Cephidae) Into Winter Wheat Fields in Nebraska

Historically, the wheat stem sawfly, Cephus cinctus Norton was a pest in spring wheat-growing regions of the northern Great Plains. However, in the 1980s, it was found infesting winter wheat fields in Montana. Infestations were first detected in western Nebraska in the 1990s, and have since spread throughout the Nebraska Panhandle. Larval damage occurs from stem-mining, but stem girdling that results in lodged stems that are not harvested results in the greatest yield losses. The biology and phenology of the wheat stem sawfly are well described in the northern portion of its range, but they are lacking in Colorado, southeast Wyoming, and Nebraska. In this study, the phenology and dispersal of the wheat stem sawfly in Nebraska winter wheat fields is described using sweep net and larval sampling. During this 2-yr study, adult activity began on May 23 and ended on June 21. Adult sex ratios were 2.32 males per female in 2014 and 0.46 males per female in 2015. Both sexes demonstrated an edge effect within the wheat fields, with greater densities near the field edge. The edge effect was stronger for male wheat stem sawfly than females. Wheat stem sawfly larval density also had an edge effect, regardless of the density of female wheat stem sawfly present. This information will be useful for developing management plans for the wheat stem sawfly in Nebraska and neighboring regions.

Respiration and C dynamics in Poplar roots

&lt;p&gt;Large amounts of C are allocated to tree roots, but little is known about the age and dynamics of their non-structural C (NSC). We measured bomb-radiocarbon (&lt;sup&gt;14&lt;/sup&gt;C) in respired CO&lt;sub&gt;2&lt;/sub&gt;, non-structural (mainly sugars), and structural (cellulose) C in roots. The steady decline of &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C in atmospheric CO&lt;sub&gt;2&lt;/sub&gt; since the 1960s indicates the mean time elapsed since the C in these pools was fixed. We measured coarse (&gt;2 mm, mean 2.91 mm) and fine (&lt;2 mm) roots from 12 German poplar trees sampled before and after girdling of 6 of the trees. All samples were taken in 2018, an exceptionally dry summer in Europe. The mean &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C &amp;#177;SD of root-respired CO&lt;sub&gt;2&lt;/sub&gt; (4.1 &amp;#177; 3.6 &amp;#8240;) in June-July was equal to current atmospheric &amp;#916;&lt;sup&gt;14&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt; (1.2 &amp;#8240;), irrespective of the mean age of root cellulose. During extended incubations, the &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C of root-respired CO&lt;sub&gt;2&lt;/sub&gt; increased to ~10 &amp;#8240; 8 days after harvesting and up to 42 &amp;#8240; 17 days after harvesting. The mean &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C of soluble sugars in the roots was ~21&amp;#160;&amp;#8240;. In September-October, almost three months after girdling, roots from girdled trees respired CO&lt;sub&gt;2&lt;/sub&gt; with &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C of 7.9 &amp;#177;&amp;#160;6.6&amp;#160;&amp;#8240; vs. 2.3 &amp;#177;&amp;#160;6.1&amp;#160;&amp;#8240; in the ungirdled control trees. However, in both groups the respired CO&lt;sub&gt;2&amp;#173;&lt;/sub&gt;-&amp;#916;&lt;sup&gt;14&lt;/sup&gt;C correlated with cellulose-&amp;#916;&lt;sup&gt;14&lt;/sup&gt;C (R&lt;sup&gt;2&lt;/sup&gt; = 0.37, 0.26 for girdled and control trees, respectively), suggesting that roots respired more stored C in the later growing season in this drought year, independent of treatment. The &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C values of soluble sugars were correlated with the &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C values of the cellulose (R&lt;sup&gt;2&lt;/sup&gt;=0.83). On average, C in sugars was fixed more recently than cellulose, suggesting mixing of young C from other parts of the tree into the roots. Stem girdling did not affect the &amp;#916;&lt;sup&gt;14&lt;/sup&gt;C of soluble sugars. Average total sugar concentrations (sucrose+ glucose+ fructose) were ~42 mg g&lt;sup&gt;-1 &lt;/sup&gt;and did not vary with sampling date, root class or treatment. Starch, measured only in September-October, was higher in coarse than in fine roots (12 vs. 3.8 mg g&lt;sup&gt;-1&lt;/sup&gt;). Respiratory loss of C was higher in the fine roots (~4 mgC g&lt;sup&gt;-1&lt;/sup&gt; day&lt;sup&gt;-1&lt;/sup&gt;) than coarse roots (~2.4 mgC g&lt;sup&gt;-1&lt;/sup&gt; day&lt;sup&gt;-1&lt;/sup&gt;), with no effect of girdling or sampling month. When normalize (expressed per gram dry root material), the NSC reservoirs and C loss rates suggest C turnover rates are 2-fold higher in fine roots than in coarse roots. The extended incubations indicate that detached roots are able to quickly utilize stored NSC, as indicated by the sharp &amp;#916;&lt;sup&gt;14&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt; increase. In comparison, stem girdling had no measurable effect on respired CO&lt;sub&gt;2&lt;/sub&gt;-&amp;#916;&lt;sup&gt;14&lt;/sup&gt;C, suggesting internal re-allocation of C from the lower stem base or large roots to smaller roots, and/or lower than expected metabolic consumption of C in reaction to girdling or because of the exceptional drought.&lt;/p&gt;