The geographic range of Figure 1
Phenological studies could be used, for example, in research on the coexistence of species (Fargione & Tilman 2005), their invasion (Wolkovich & Cleland 2011), expansion (Szmeja et al. 2016) and reaction of populations and communities to climate change (Fitter & Fitter 2002; Menzel at al. 2006; Cleland et al. 2007; Święta-Musznicka et al. 2011), especially close to their geographic range limits (Chuine & Beaubien 2001; Schwartz 2003). The main focus of research has been on the timing of periodic events, such as leaf formation, flowering, fruiting or wintering, which in the case of aquatic plants is mainly dependent on temperature (Hutchinson 1975; Szmeja & Bazydło 2005; Gałka & Szmeja 2013; Szmeja 2010). Shifts in species phenology can occur due to a rise in temperature (Walther et al. 2002; Cleland 2007); therefore, phenological data could be useful for estimating the biological effects of the recent climate warming.
Although there are various conceptions regarding the cause of global warming, we suggest that in NW Poland it could be associated with an increase in the intensity and frequency of the positive phase of the North Atlantic Oscillation (NAO), during which warmer and moister air has been flowing from above the Atlantic to Northwest Europe, Scandinavia and the Baltic Sea region since 1989, especially in colder seasons (Hurrell 1995; 1996). One of the consequences of the recent climate warming in the studied area, i.e. near Gdańsk, is the expansion of
Our objective was to examine the timing of periodic events in the population of
This study was performed in 15 watercourses with
Three 0.5 dm3 samples of water and sediment per site were collected from aggregations of
Characteristics of the age stages (morphological development stages) were determined on the basis of 728 modules of
Phenological data were collected from permanent plots (0.5 × 0.5 m) every 14 days during the whole growing season (from March to November) in 2014 and 2015. In winter, samples were collected every 30 days. On each sampling occasion, the temperature of water was measured and the number of modules as well as their age stages (juvenile, mature, generative, senile, winter bud) were counted (without plant removal). On the basis of the quantitative dominance of the age stages, the phenological phases were established in the development of the studied population.
The watercourses with
Water characteristics at the sites (1–15) of Explanations: Cond. – conductivity, PAR – light intensity, median for pH; mean ± standard deviation for remaining traits
Trait
PH
Cond.
Calcium
Total nitrogen
Total phosphorus
Water color
Flow
PAR
Site
(μS cm−1)
(mg Ca dm−3)
(mg N dm−3)
(mg P dm−3)
(mg Pt dm−3)
(m s−1)
(%)
1
7.7
272 ± 25
59.4 ± 1.2
2.6 ± 0.2
0.1 ± 0.0
20±3
0.5 ± 0.01
42.4 ± 1.2
2
7.9
257 ± 8
57.8 ± 1.0
2.2 ± 0.2
0.4 ± 0.0
19±1
0.2 ± 0.00
58.3 ± 4.6
3
7.2
197 ±13
44.4 ± 0.3
0.7 ± 0.3
0.1 ± 0.0
28±3
0.3 ± 0.02
43.4 ± 3.2
4
7.6
290 ± 23
58.6 ± 0.0
1.1 ±0.2
0.3 ± 0.1
26±8
0.4 ± 0.06
50.2 ± 3.4
5
7.3
206 ± 9
54.8 ± 3.5
0.4 ± 0.1
0.4 ± 0.1
18±6
0.1 ±0.01
73.5 ± 2.6
6
7.3
270 ± 23
67.3 ± 1.1
1.0 ± 0.1
0.1 ± 0.0
40±6
0.2 ± 0.03
94.9 ± 3.3
7
7.8
220 ± 35
41.7 ± 1.2
1.5 ± 0.9
0.2 ± 0.2
7 ± 1
0.5 ± 0.09
44.8 ± 1.6
8
7.5
255 ± 28
45.2 ± 1.7
1.5 ± 0.8
0.5 ± 0.2
21 ± 1
0.2 ± 0.06
45.9 ± 5.1
9
7.8
185 ±19
46.0 ± 0.2
1.5 ± 0.3
0.1 ± 0.0
20±2
0.1 ±0.01
70.7 ± 2.7
10
7.5
214 ± 19
42.2 ± 0.4
1.7 ± 0.2
0.2 ± 0.1
55±4
0.7 ± 0.02
68.8 ± 6.0
11
8.0
220 ± 12
77.0 ± 0.3
1.6 ± 0.5
0.3 ± 0.1
15±5
0.3 ± 0.02
49.9 ± 2.4
12
7.7
269 ± 21
61.3 ± 4.3
2.9 ± 2.2
0.4 ± 0.3
13±3
0.3 ± 0.07
64.6 ± 1.4
13
7.7
340 ± 47
62.1 ±0.3
0.9 ± 0.1
0.2 ± 0.1
29±6
0.3 ± 0.05
54.0 ± 0.4
14
7.2
231 ± 16
45.5 ± 0.4
1.0 ± 0.1
0.2 ± 0.1
15±3
0.1 ±0.01
44.3 ± 0.8
15
8.7
332 ± 24
56.6 ± 0.8
1.7 ± 0.3
0.3 ± 0.1
25±2
0.1 ±0.01
36.8 ± 1.7
Alpine pondweed is a non-evergreen submerged perennial plant. We described five age stages during its development: juvenile, mature, generative, senile and the resting stage as a winter bud (Table 2, Figs 2 & 3).
Age stages of Figure 2
The number of age stages in the populations, where: J – juvenile, M – mature, G – generative, S – senile age stageFigure 3
Characteristics of age stages (J–S, where: J – juvenile, M – mature, G – generative, S – senile) and the time of their residence in the population, on the basis of 728 plant samples Explanations: n – number of samples, ± – arithmetical mean with standard deviation, and min.–max value of the trait
Trait/Age stage
J
M
G
S
No. of samples
79
482
125
42
Height of shoot (cm)
4.5 ± 2.0
32.1 ±23.6
54.9 ± 32.4
15.0 ± 15.9
(1.2–13.0)
(3.5–185.5)
(19.5–173.5)
(1.1–66.0)
Number of leaves
2.3 ± 2.4
11.5± 3.3
14.2 ± 3.2
2.3 ± 3.1
(0–7)
(4–22)
(7–23)
(0–9)
Biomass (mg d.w.)
13.4 ± 12.3
43.1 ± 23.4
70.3 ± 29.9
16.8 ± 14.9
(1.8–62.3)
(5.6–136.1)
(13.7–180.5)
(2.0–68.5)
Allocation of biomass to stem (%)
28.7 ±21.5
22.3 ± 9.2
28.9 ± 8.0
44.4 ± 20.8
(4.0–95.5)
(3.3–62.7)
(13.6–57.1)
(7.4–90.4)
Allocation of biomass to rhizome with roots (%)
53.8 ± 20.2
20.9 ± 14.4
9.3 ± 6.4
38.5 ± 23.0
(4.5–96.0)
(2.1–82.1)
(1.2–47.0)
(7.9–92.6)
Allocation of biomass to leaves (%)
17.5 ± 19.9
56.9 ± 13.4
57.4 ± 9.8
17.5 ± 24.3
(0–71.4)
(12.0–88.0)
(24.4–77.4)
(0–71.5)
Allocation of biomass to generative structures (%)
0
0
4.9 ± 5.2
0
(0.1–38.0)
Residence time (weeks)
28
18
12
16
Week in the year
12–40
22–40
24–36
30–44
Temperature of water (°C)
13.9 ± 5.23
16.3 ± 4.23
18.2 ± 3.46
13.1 ±6.12
(5.2–24.5)
(8.3–24.5)
(13.0–24.5)
(3.4–24.4)
In spring, the winter bud develops into the juvenile stage, which is 4.5 ± 2.0 cm high. The shoot consists of a thin stem with a few small leaves, together with a fragment of the rhizome. The fragment of the rhizome constitutes most of the biomass of an individual (53.2 ± 20.8%), the rest being the stem and leaves.
Adult
The generative stage of development, i.e. flowering and fruiting, consists of the underground rhizome and the aboveground shoot, which grows to a height of 54.9 ± 32.4 cm, consisting of the inflorescence spike and 14.2 ± 3.2 leaves, including 3.3 ± 1.7 leaves floating on the water surface. The arithmetic mean of the dry weight of this developmental stage is 70.3 ± 29.9 mg, including 54.7 ± 9.8% leaves, 28.9 ± 8.0% the stem, 4.9± 5.2% the inflorescence (with peduncle), and 9.3 ± 6.4% the rhizome with roots.
Dieback of the aboveground shoot, fragmentation of the rhizome and formation of the winter buds is characteristic of the senile stage. The dry weight of the shoot is 16.8 ± 14.9 mg, where leaves accounts for 17.5 ± 24.3%, the stem for 44.4 ± 20.8% and the rhizome for 38.5 ± 23.0%. The resting stage of the studied plant is the winter bud, and it plays the functional role of the turion. The latter stage, which develops on the rhizome, lasts throughout the winter and is small (1.3 ± 1.1 cm) and light (2.4 ± 3.5 mg d.w.).
During the year, five phenological phases were identified in the populations of
Development of Figure 4
The growth phase starts in week 12 (early spring), at a water temperature of 5.4 ± 0.16°C. It lasts approximately ten weeks and the mean water temperature during this period is 8.5 ± 2.41°C (5.2–11.8°C). At this time, juvenile shoots grow from winter buds, forming rhizomes and consequently modules, i.e. repeating structural units of clones (individuals). In the growth phase, juvenile shoots proliferate and dominate in the population.
The maturation phase begins in week 22 at a water temperature of 13.9 ± 0.85°C. It lasts only approximately two weeks, with a median water temperature of 13.7 ± 1.28°C. In this phase, new young modules are formed; their height and the number quickly increase and the rhizome becomes thicker. Consequently, the population density increases, whereas patches of
Reproduction starts in week 24 at a water temperature of 15.6 ± 1.04°C, and it lasts approximately twelve weeks, with a median water temperature of 18.9 ± 3.23°C (14.0–24.5°C). At this time, the predominance of fully developed flowering and fruiting shoots with floating leaves is observed in the population, which stabilize the inflorescence stem and keep it over the water surface. During this phase, patches of
The first clear signs of senescence in the populations are observed in week 36 at a water temperature of 13.7 ± 0.77°C. At this time, there are juvenile and mature modules in the population, but no longer generative ones, because the inflorescences and infructescences detach from the shoot. In week 40, senile modules with yellowed leaves occur in the population, which eventually decompose (decomposition of leaves, fragmentation of the rhizome). The last aboveground senile shoots occur in the population up to week 44 (water temperature 6.3 ± 1.05°C), when the season comes to an end.
From week 44 to week 12 of the next year, the winter dormancy phase (diapause) occurs in the population. At that time, the plant overwinters as winter buds with fragments of the rhizome. The environmental trait that significantly separates the presented phenological phases is water temperature (
Areas located in temperate climates are characterized by seasonal phenomena in plant populations, which very often makes them the object of phenological studies. An example of such research might be the course of periodic events in the development of
An increase in global air temperature does not raise serious concerns (Hurrell 1995; 1996; Stocker 2014). The globally averaged, combined land and ocean surface temperature data show a warming of 0.85°C during the 1880–2012 period (Stocker 2014). In N Poland, as in most of the Baltic basin, the warming has been particularly strong since 1980. In the period from 1980 to 2010, the annual air temperature at the weather stations located along the south Baltic coast rose by 0.104°C per decade (Marsz & Styszyńska 2010). The mean annual air temperature near Gdańsk rose from +7.0°C (during the period of 1851–1988) to +8.2°C (between 1989 and 2009). The increase in annual temperature during the present warming (after 1989) is largely due to a sharp temperature rise in winter and spring, mostly in March and April (Szmeja et al. 2016). Air temperature influences environmental conditions in water bodies, for example by regulating the length and timing of the period of ice, temperature of the surface layer of water (Wetzel 2001), and duration of the growing season of plants, as well as the rate of growth and development (Szmeja et al. 2016). There is a close relationship between air temperature and water temperature. The correlation coefficient between the average monthly temperature of the air near Gdańsk and that of the Baltic waters in the area is high and usually 0.85–0.90 (Marsz & Styszyńska 2010). The correlation between the temperatures of air and water in watercourses with
Terrestrial plant species growing in similar regions have developed a similar phenology (Thuiller et al. 2004). Additionally, previous studies on aquatic plants, as presented by e.g. Santamaria et al. (2003), show that patterns in the phenology of plant species usually correlated with certain environmental variables, such as temperature, precipitation, latitude or altitude. The results of these studies show that most